I use vim with a tab autocompletion macro, and sometimes I really do want to insert a tab character and autocompletion gets in the way.Today I found out that if I hold down shift and hit tab, a tab is inserted and tab autocompletion doesn't get triggered. Prior to this I have been adding a space then hitting tab, which leaves ugly little space-tab sequences in my files.
Hope this helps some one out there.
Cheers,
Steve