If you happen to use gitk and Ubuntu 9.10 with desktop effects, you might notice that gitk and other tk-apps tend to look like crap (i.e. giant fonts, buttons, etc), rendering them useless.
I found the solution for this in a blog entry of the Navarra Group. All you have to do is
sudo aptitude install tk8.5 and
sudo update-alternatives –config wish (here you select wish 8.5 from the list).