Naturally when engaging in a business venture, it's prudent to do a bit of research.
Estimating sales figures for Xbox Live Community Games has proven to be a pretty tricky task. The closest similar market is naturally Xbox Live Arcade, and even here sales figures are seldom publicly announced. VGChartz.com does a good job of estimating sales based on a clever web-crawling methodology, but it's still not accurate.
An enterprising chap on the XNA Creators Club forums has come up with another polling tool that checks the Xbox Live Most Popular list on a regular basis. Based on this we can work out approximately what sales volume Community Games are achieving, by comparison to estimated figures for XBLA titles adjacent in the rankings. Current data suggest that Community titles may be selling at levels equal to 20th best-selling Arcade title, which is no mean feat at around 2,000 copies in an average week.
There's a caveat to that, however. There's speculation that these popularity lists aren't entirely accurate in the first place, and that it's counting trial downloads as full game downloads.
Our research has shown so far, on admittedly small samples, that we can expect Community games as a whole to achieve around 15% of Arcade sales. The market shows clear sign for expansion as a significant proportion of respondents had not even checked out the Community Games Marketplace, and others still said that they'd be more inclined to spend points on a larger number of cheap titles.
In conclusion? I'm concerned for the developers basing business decisions on the optimistically-high popularity-based figures, and all developers would do well to market not only their wares, but also CG initiative as a whole in order to reach 'unconverted' market potential.