I second what fatalsaint says. If you are looking for a regular desktop and more desktoppy applications, easy debian is the way to go. The other OSes aren't really usable yet.

That said, if you still want to go for it, you can check out my docs on installing Mer and Fedora on the N900:
http://wiki.maemo.org/User:Jebba/Fedora
http://wiki.maemo.org/User:Jebba/Mer