The source being available is no reason not to write documentation. - True. Doesn't stop me from being lazy.

The fact that POD makes it particularly easy to document... - I'd forgotten about POD, it's so much part of my perl, it is perl.

I should also add that even if you don't plan to release your code, writing some documentation is "best practice", it will save hours of irrtation when you need to hack some of your old code.