Group Chat sounds good. Sounds like something N900 should have.

You can download an app to send files over IM conversations but yes a native built in solution is probably better.

Though I would say comparing N900 to Apple, and BB to Nokia in this area is a bit over the top. Nokia's chat implementation is quite well done. Not having to install Skype, Gchat, yahoo etc and being able to log into all your IM accounts with 3 clicks is superb (though not perfect).