Seems like there's a potential for a (productive?) arms race here: services like Twitter or Facebook might (and presumably already do) algorithmically try to identify fake users. That evolutionary pressure will generate more sophisticated bots...
Considering Twitter didn't react to Quora registering so many accounts they had to use a crowdsourcing service I don't think they care that much about bots.
I think may speak more to Quora's connections than Twitter policy. I know of several startups that had legit accounts suspended because of supposed botlike behavior (things like they had a music venue discovery service and were making a twitter acct for every major city in the US).
Could be a real time saver, and of course the definition of a 'bot' can become squishy as in, "I've got an application that tweets as me for some things." Technically a bot, useful as an assistant?
A much more interesting question is the believability. For older folks there seems to be a great willingness to trust what is written on official looking blogs, whereas my kids naturally distrust such blogs, and yet if the folks they are following are all in favor of some trend there is a tendency to see validity in the trend.
Its clearly a more complex subject than I ever gave it credit for before.
Over the next 10 years I see us leaving the age of the spammer and entering the age of the bot. By that I mean that bots will become so useful to us that even when we know they are bots we'll still welcome their company.
Frankly I find dedicated bot accounts less objectionable than human accounts where a bot or application is inserting paid commercial messages into the tweet stream, even if they're marked as such. (See adly.com) (Can someone make their twitter client screen all tweets with #ad?)
I think part of the issue is, does Twitter consider this a violation? As a communications platform successor to e-mail, are machine-generated messages necessarily "bad" simply because they are hijacking a 1:1 channel? And does a broadcast message violate the spirit of Twitter as a comms platform?