yes

It's very very useful, I need to use it more. One can do an entirely piece just with the Appearence pannel, I've seen a lot of tuts covering it on VectorTuts+!

interesting results I must say, it seems your followers are either all for it or don't use AI

All the time. I use it mainly on strokes. In CS when you would pick out your brush, set its size and opacity, when you went to make another stroke it would carry over onto the new path without having to re-apply it. CS4 doesn't handle it the same way, it just defaults back to a regular stroke that uses the same color, so I use styles instead.

of course, its the best thing ever

also considering AIs future abilites in web design, it is probably one of the best things about it