It's not always easy working largely in isolation as a freelancer, but I do bounce a lot of ideas off the ol' hubs. With the heart of a scientist and the keen eye of a designer, I really value his opinion. I find that when I am doing work for myself, as in the ad campaign I'm working on, I won't quit until I come up with something that passes his scrutiny. I simply ask him to answer: a) Yes! (the exclamation point is key), b) No, or c) Maybe, with revision (though I always get more feedback than this).
It wasn't easy, but I finally got an "a)" with this design: