I used to use POD for all kinds of documents. But I was never quite satisfied that POD still has a lot of ugly markup. I guess some may consider this a sacrilege, but I think reStructuredText is both easier to read in pure ASCII form and is more expressive when translated to HTML (yes, you do need a Python interpreter to convert reST to HTML).

I still use POD for everything related to documenting Perl code, but use reST for things like functional specs.