Still on the fence

A question --- if the user opts for the Toolbar option, does it use AJAX like other areas of the site to predict/finish the username? Like when you send a PM for instance, how it pops up with the usernames as you type.
I'm just concerned to spend money on this and then find people have type-o's in usernames. I was talking to one of my mods about this and he kept leaving out the space in MY username when I was showing him how to use it. So if a mod even has trouble...
I really want this, I think it could be great to increase social networking on the site itself. It's a shame it couldn't work in-line in the editor itself, as you type (just like I am typing this post right now), if it detected @ it could start displaying usernames as someone typed

I wonder how facebook does it.
Mike