I seem to have had more votes (and thus, higher payouts) when I voted up my own posts.

If you have a decent amount of SP, voting on your own post can also give it some extra exposure, people tend to read posts that have some payout as they see other people must have valued it, so they go and take a look too.

I think people are more inclined to look at a post that has $20 than one that has $0.01