Introducing the Innovator's Patent Agreement
Note: Emphasis is mine.
"We will implement the IPA later this year, and it will apply to all patents issued to our engineers, both past and present." 
"The Innovators Patent Agreement (IPA) is a new way to do patent assignment that keeps control in the hands of engineers and designers. It is a commitment from a company to its employees that patents can only be used for defensive purposes. The company will not use the patents in offensive litigation without the permission of the inventors. This control flows with the patents, so if the company sells the patents to others, the assignee can only use the patents as the inventor intended." 
Now look at the names on the patent in question. Do you think they'll oppose offensive litigation specific to this patent?
Also note that nothing in the IPA prevents the use of patents offensively if the named inventors agree.
In effect, the IPA isn't relevant to this patent, as the named inventors haven't (and probably won't) make a commitment not to use it to protect their business/personal interests.
i.e. Twitter sues Company X for using a follower system. Company X asks judge to throw out the complaint based on the Innovators Patent Agreement that the Twitter CEO and board signed.
In law, it is very difficult for individuals to bind their future selves. You generally need another party to create obligations that they can enforce against you. So for example counter-parties to a contract, trustees and beneficiaries, employers and employees, fiduciary agents and their clients etc etc. All of these require distinct legal persons to work, if you you combine them into a single legal person the obligations evaporate.
Because when it's you vs you the law pretty sensibly throws its hands in the air and says "well what the hell do you want the courts to do? Hop in a time machine and drag past you into court?"
And there we have the invention of live-tweeting an event!
emphasis on past
The heaps of similar methods that don't include follower/following is a good reminder of how easy it is to avoid infringing on this patent: just skip the follower/following mechanic.
LJ was the direct inspiration for Twitter, at least according to this interview: http://latimesblogs.latimes.com/technology/2009/02/twitter-c...
Or did LiveJournal have a way for me to be your friend without you being mine?
Not in Livejournal lingo - remember, this is pre-Facebook.
Livejournal's 'friend' and 'friend of' worked exactly the same as Twitter's 'following' and 'followers'.
And apparently I'm getting downvoted for not being familiar with LiveJournal, so that's something someone else would have to do.
I would be tempted to say that automated agents would obviously be prior art, but inventions that just automate long-standing physical workflows in a straightforward way (do it on a computer) have been found patentable more than a few times.
So I wouldn't be optimistic that the reverse isn't also true.
I am just too thick to understand IP law.
Whole thing sucks. I'm not going to read the patent.
As others remarked, IRC is follower-based. You follow a bunch of channels by sending subscription message (JOIN #channel-name) to central authority (IRC server). The server keeps track of who follows which channel, and brokers any PRIVMSG #channel message messages to the followers, until the person does PART #channel-name or disconnects. Aside of that, a direct person-to-person mechanism exists just as well, also via the PRIVMSG command.
The USER nickname command provides, among other, list of (public) channels the named person follows, which some IRC clients use to allow user to follow the same channels.
Yes, there is a difference between an IRC channel and a singular persona, but it is not as clear-cut as it may seem on its face. On one hand, some channels are muted, and only admins, or just a single admin, can post. On the other, Twitter handles often stand for multiple persons, speaking for one organization, team etc.
* * *
As an IRC user, I am ashamed and appalled of how low our industry has fallen -- somebody applies for a patent for what (after cursory read seems to me) a copy of well-known and long-established functionality.
Such a simple difference makes all the difference. In this case, enough to file a patent.
If they didn't file a patent someone else would have.
And Twitter would have been in a position to object it to death.
The law went into effect on Monday.
First to file drastically reduces the number and complexity of patent disputes and it improves the stability of a patent once acquired.
And there's always been a de facto paperwork requirement under first to invent anyhow, it's just that you had to keep nauseatingly detailed "inventor's logs" just in case somebody sued you. And even then you could be bankrupted in court by someone running a frivolous interference case.
First to file is a net win. That's why everyone else on Earth has been using it.
However, if you care just enough for your website(eg. Your site makes enough money to pay for itself and then some), I would advice against approaching twitter. Chances are twitters lawyers will ask you to shut your project, if you approach. And if you don't, chances are your project might be small enough and remain unharmed(security by obscurity?) if twitter goes a-trolling.
IRC clients also notify the user when messages targeting them (via your handle, similar to @handle) are received, and I've seen scripts that pull comments from specific users from any open channels, and the opposite (namely blocking users) has been present in countless applications, which indicates the concept of paying special attention to a specific user isn't a new one.
On top of this, I don't feel like there's anything that's innovative at all in this patent. Since when did the innovation step stop being a requirement?
Their first claim is the following:
A way to communicate between computers (1:many) where users can designate by computer to follow someone else.
Where users are identified by accounts where following is an account config.
Where users can be notified of messages that they are not explicitly told about (but follow).
Where another user is marked as the sender (we have their followers, so that is implicitly marked too).
Where the first user is one of the followers.
Where the first user has devices ("endpoints") that they'd like to recieve messages from (phone/etc), this patent applies to sending each message to each of the endpoints in their appropriate format.
Points 2-8 are about:
- Different ways to send the message.
- per-following subscription preferences.
- Message preferences set up in weird ways. (3. I'm not too sure on this)
- Broadcasting through an aggregator that sends data through batched messages.
- Translating messages from/to UTF-8/etc.
- Delivering messages at specific times.
- Sending URLs to messages
At a glance, claim 9 is about storing the data for a message.
Claims 10-15 are about:
- Different ways to trigger the message that this data can represent.
- Per-following subscription preferences (I'm starting to think this is Twitter group subscriptions)
- Per-following subscription preferences including time periods.
- Messages that have no explicit recipient.
- Aggregated message delivery.
- Sending URLs to messages as the message
At a glance, claim 16 is about building the system that does this.
Claims 17-22 are pretty much the same as 10-15
EDIT: Wow, I didn't realize HN uses a variant of Markdown. (Good, good)
(The blog article was written in relation to a different patent, but the prior art is most directly related to a Twitter-like service.)
Still, this patent can probably easily be invalidated with prior art.
They are using other people's money -- given the current system, they had a fiduciary responsibility to do this, unfortunately.
Maybe the lesson is to not take other people's money, but investment really does allow grand things happen that would not happen otherwise.
Patent system is fucked and fucked corrupts absolutely. At least, that's my take away.
The claims require service to have concept of explicit following of other users and receiving messages not explicitly addressed to them, so it's not like CC: in e-mail or Jabber chats.
Would something have to meet all 22 claims to be infringing?
Matter was settled.
Can't sth like that happen in computers and Internet?
(BTW, it seems either USPO is very corrupt or very negligent. Or maybe they don't give a damn!).
Basically, there is no incentive for them to do a diligent job, so they don't.
IPv4 multicast with IGMP and any system built on it are the most obvious, not to mention any IM software where people can set their status and have it broadcasted to all contacts.