I actively enter brews in competition, so I'm admittedly biased. That said, I do recommend people enter comps for the unbiased and anonymous feedback. We have a large club and a monthly meeting, but it is nearly impossible to get an honest opinion from someone you know, standing right in front of you.
True, sometimes the written feedback is not helpful - that really depends on the caliber of the judges. You have to take the feedback for what it is, but sometimes you get something back that leads you to ask around about DMS or under-attenuated, and then you learn more about wort-chilling and yeast starters, which helps every batch you brew.
