I know that there are some N900's apps for Facebook, but I never used any of them. I use N900 same way as my PC, where also I don't have particular app just for Facebook. N900's browser behaves same way as PC's Firefox, so I don't see a point to have Facebook app, I use just browser (page stored in bookmarks). If you don't like PC look, then just go with browser on http://touch.facebook.com.