So, for the most part, I've ignored contests, because I don't need the tease in my life. However, this winter I've put aside my reluctance and entered two. One is fee-based, and the other is not (so I'm rationalizing the cost as split between them).
However it all turns out, I'm pretty happy with my decision. Winning would be awesome, of course, but the fee-based contest provided the judges' scoresheet in advance (and the criteria there were worth the entry fee by themselves), and will send comments after the judging. The free one is, well, free, and forced me to come up with a 300-word pitch that I'm pretty proud of. And both made me go back through the MSS and tweak, resulting in a stronger product.
So, wish me luck, and if you're thinking of entering a contest, pick the right one and pray about it. Don't get your hopes up, but view the contest as a chance to really polish your book and perfect your pitch. If anything comes of my entries, I'll be sure to let you know!