Are Freelance Web Sites Useful?

GrokSoup asks: "There is an article [registration required] in a recent Wall Street Journal about the rise of freelance sites like eLance, Guru.com, FreeAgent, and HelloBrain. While I've looked at these things before, I've never used them. Have many Slashdot-ers used them for tech freelance work? What kinds of experiences have you had? Think they're useful? "