PlayNoEvil keeps an eye on skill gaming - playing for cash, and (usually) in a different category than straight up gambling - and points to SkillGround, which has some new offerings, including a fighting game, a FPS, a racing game, and more in the pipeline. Of course, with money comes problems - particularly because some of these games are particularly vulnerable to all manner of bots.
There are some interesting risks for online skill games. First, "turn-based physics" games like golf, darts, and pool are very conducive to "analytic bots" that find optimal shots or allow players to test shots before they take them.
Second, these games can face serious threats from automated play bots. The "twitchy-er" the game, the more vulnerable it is going to be to botting... and unlike regular game models, there is a powerful incentive to attack these games.
He also notes that there's a lot of potential in this market for game types, as well as having a potential impact on the market as a whole. I don't really get the appeal of most forms of gambling/betting/etc., but I suppose if you're looking for a way to bring in some cash (or lose a lot of it) while playing games, it's one option to look into.