"@example.com/abc" is one (not particularly nice) way of doing it, but I'm struggling to think of any way that would work nicely.
The obvious 'let's use email instead of that @you thing' would make implementation really non obvious, because it dramatically changes the @ role from the current usage: @ means 'adressed to', not 'residing at' like email/xmpp.
I'd reverse the order, which would read much better and follow known ordering conventions (FQDNs, email...):
email tag syntax inspired: @abc%example.com. That would be @marcoarment%twitter.com and @marco%app.net.
FQDN inspired: @abc.example.com looks much better. That would be @marcoarment.twitter.com and @marco.app.net. It would follow the convention that a non qualified name belongs to the local net. I don't know how that could possibly extend to actually integrate with DNS itself, so that a something-record @marco.marco.org. would resolve to the service handling marco's status stream, MX style.
You will soon be able to use your own domain names so ^https://example.com will be possible.
This kind of works. Ideally I'd like to drop the leading @ but I guess that'll be hard to do.
We could go oldschool with a newline:
More seriously, I wish there was an easy way to divorce the username from the server similar to how DNS works so I could move my provider without losing my identity. A separation of name providers and service deliverers would do this.
Also, do we need names to match domain names? Couldn't we start from scratch?
It would be interesting to see what we could come up with if we dropped .com, .net, .org, .name etc and went for something more abstract.
.blue .horse .cheese .bang
That domain does not have to be the server they use for microblogging or whathaveyou. It shouldn't be, honestly. You can host your identity anywhere and point to the microblogging server using a link.
So, I can be firstname.lastname@example.org, as familiar as an email address which is REALLY important for usability; the UI can drop the domain if you think it is ugly or hinders readability, and we go on from there.
This is what webfinger + xrd gives you: http://code.google.com/p/webfinger/wiki/WebFingerProtocol
It's already used by status.net, rstat.us, etc etc. tent.io ignores it and wants to reinvent everything.
Now I can switch microblogging sites if I want by just pointing to a new one. But, just like changing your name is a hassle in real-life, changing where your identity is held is also hard. Using DNS and having your own server for at least your identity are ideal.
What's wrong with email@example.com?
Using the same means of locating a person seems very very reasonable from both a technical aspect (it works for them just fine) and from the viewpoint that people already understand that an email address represents somebody's online presence and this is how you can communicate with them. Concept familiarity is extremely important for adoption, so that should be considered.