You thing the browser is what makes the N900 not a smartphone? Its nothing many Android and WebOS devices won't soon be replicating. Its really about the class of OS the N900 is running. It has the same app frameworks and components of a desktop Linux distro, meaning less limitations. Robustness is the applicable word here.
Now I'm shocked you missed the multiple Twitter options. From editing the Twitter webpage using a Greasemonkey script, web apps like Hahlo, native apps like Witter or Mauku, or the Conversations plugin, there are multiple options!
Video chatting is possible using aMSN or if you recieve a Gtalk video conference, and it works very well. Was it not to your liking?
You have to be more realistic, and know that the promise of nirvana with Maemo/MeeGo is tied to Symbian^4, which is still months away. Once S^4 and MeeGo are launched and the ecosystem broadened, apps will pour in.