As a previous poster noted the great thing about the N900 is the plugins to the maemo platform that enable so many features. Photo sharing and chat are plugged in to the system directly, there is a widget showing my friends status updates all day long, when I touch that it launches lite.facebook.com which is very good on the N900 and gives me access to every feature of facebook that I need (I don't play any of the farmville games etc).
I have an ipod touch and always use that to compare experiences with my N900 and I much prefer using the N900 than the iPhone facebook app.