You guys got lucky. I bought six pair of the knog knockoffs (so like... $20), at least one was DOA, 4 sets of them lasted less than a dozen uses each, and the 6th set is still going strong after a couple months. None of them ever got wet or stepped on, the just started failing at the solder joints after a couple weeks.
I'm assuming this means I have more data points than you gize, so:
The good thing about 'em is that at only a few bucks, you can afford to buy 6 to get 1 good one.
You seem to be in the minority here... the general opinion I've heard everywhere is that dealextreme is the way to go for bike lights