Opened a file with tabs used instead of spaces? Even just one or two? Instead of feeling like an ogre on a rampage just use:
That's it, disaster averted ;-)
Make sure you have this set in your .vimrc:
That is so much better than using %s/\t/ /g!!!!
Note, that this only works if you have :set noexpandtab
Thanks @kid-icarus I've update the tip :-)