A Photo Editor has an interesting post on photography contests http://www.aphotoeditor.com/2009/01/23/the-biggest-scam-in-photography/trackback/
I've never entered photography contests as such, but I'm considering doing so in 2009. One problem is that many take eternal non-limited rights to not just the winners, but to all entries (read the fine print). On the other hand, local juried exhibitions are limited both in number, in jurist, and in competition.