Correspondence chess

What is the value anymore of corr chess? I don't ask this frivolously, as I've just finished my second corr tournament (+3 =2 -1, 2nd place) and am unsure as to whether I should start another one. They are fun in a sense, but there is no practical way to stop cheating and I can't help but feel in some of my games that I'm playing against a computer. As much as I like the analytical practice and the use of very sharp lines, it's very disheartening to think I may be playing Rybka. Since we have the anonymity of the internet, has anyone ever cheated at a corr game, and would you be willing to cop to it? I'm just trying to get a feel for how many people play fair.