With video games going more and more mainstream -- and with plenty of demographically prime mid-20s players -- it should come as no surprise that TV viewership honcho Nielsen is planning a service to gauge who's playing games.

Next year, Nielsen Media Research will launch its GamePlay Metrics service, which will collect ratings for video games. The numbers should help add greater credibility to the developing in-game ad market, which is forecast to reach $730 million by 2010, according to The Yankee Group.

That's a lot of quarters ...