It's surprising how few applications are needed once you have a decent operating system underneath (see the images below). OpenOffice, FSpot and Tomboy should probably be there as well, but I don't need them at the moment.
Compared to OS X, Linux/Ubuntu is missing a good feed reader (NetNewsWire), a blogging tool (Ecto), a calendar (iCal), and a few specialised applications like OmniGraffle and OmniOutliner.
Compared to Windows, Linux/Ubuntu is missing all the audio and video tools (FruityLoops, SoundForge, Acid, Reaktor, Tag&Rename, dbPowerAmp Music Converter, VirtualDub etc).
