I can't believe no one has said this yet, so here's my advice. You're obviously not sure, which means you can see that the N900 is a valuable device and has potential and is a much nicer environment and ecosystem as far as community etc are concerned.
Stop installing things from extras-testing or extras-devel. Once you've flashed your device. Install your essential stuff (AIM) from normal extras repository to minimalise a sore head. Once you've reached extras capacity and you're feeling brave, maybe you see something in extras-testing or devel you like, enable those repositories, make a coffee whilst the package list updates. And one-by-one install the new potentially unstable application, test it, give your feedback if something isn't working, etc, etc.
btw, AIM? You're kidding :P I don't know anyone that uses that rubbish service :P Come into the 21st century!