i remember it was a pretty big topic after twitter changed (hijacked) the RT convention. there was an outcry because twitter justified it at first with "UX streamlining", but as a matter of fact it was a scalability issue. (or maybe i'm mixing up two different controversial decisions by twitter into one...)

... but everyone got used to it and the .@ convention was adopted pretty fast.

update: this is the "usability feature" http://blog.twitter.com/2009/05/small-settings-update.html

this is the truth http://blog.twitter.com/2009/05/replies-kerfuffle.html

this is the actual hijacking http://blog.twitter.com/2009/03/replies-are-now-mentions.htm...