The N900 is still pretty new, but there is a decent selection of apps that are ready and stable, and lots more coming down the pipe, so to speak. As the previous poster said, the App Manager is the place to go; the website is just a prettier frontend to it. On that topic, the App Manager could probably use a makeover, but installing and removing apps should be fairly straightforward. Its heritage is Linux's package management system which (to put it very imprecisely) is kind of like the "app store" model in that everything is centralized (rather than random "setup.exe" files scattered across the web). Any applications that are ready and tested will show in there, and both system and application updates can be downloaded through there as well. You may hear of upcoming apps being in extras-testing or extras-devel -- don't mess with those if you don't know what you're doing, or if you want your phone to work