Look, the standard rules apply: use your best judgement before posting. That means try to keep OT posts down, but if you have something cool to share that isn't about D&D, that's probably okay.
The thing that isn't okay is posting lots of pointless OT stuff because you're just bored. That, and spam, should be avoided. I think most people have a really good sense of what is appropriate, so it's almost never a problem.
Earlier today, though, there were four or so totally OT polls, and that was inappropriate.