I just upgraded to Ubuntu Gutsy from Feisty (which went as smooth as all my Ubuntu upgrades over the past year - more to blog about this later), but a slight "oh, crap" moment when I started to have at some coding and I realized vim was feeling crippled and refused to load my plugins.
The Ubuntu upgrade brought along vim 7.1, previously I was on vim 7.0. The simple problem was my runtimepath in my vimrc. One of the paths pointed to the Ubuntu installed /usr/share/vim/Vim70, which was now really /Vim71.
I couldn't find any error messages and there was no visual clue that vim was having a problem processing the rc file (that I could tell). It just didn't load everything that it should have.