I had folding just stop working in my Python sources... without a rhyme or reason. The fix was't immediately obvious and I did not find an answer on SO... I'm using spf13vim and I have tried set foldmethod=indent six ways to Sunday and no dice... I have nothing else futzing with folding in my .vimrc.local and I have already tried updating spf13vim although the problem just started willy nilly while I was coding after writing my buffer to disk.
When folding (or anything) goes awry in VIM, whether you have spf13vim or any other elaborate .vimrc mod, begin with this...
rm ~/.vimviews/*
...and restart vim. It cleared this problem up with magic. I hope this helps someone stay young.