I’ve recently taken a shine to Picasa as an alternative to F-Spot on Linux. Installing Picasa 3 Beta for Linux is straightforward on Ubuntu: download the .deb from Google’s site and then install it (sudo dpkg -i picasa_3.0-current_i386.deb). Having done that, the only other bit of configuration I have found useful is to change the default application for photo-media handling in Nautilus. To do so, launch Nautilus > Edit > Preferences > Media > Photos > Open with other application… and then choose /usr/bin/picasa. Job done.
If you want a flamey discussion of the relative merits of F-Spot and Picasa (and gThumb, digiKam etc.), see this thread.