The February '06 issue of Game Developer Magazine (hey -- the last magazine I founded that is still in publication) has an article on "Casual Games and the Mass Market." They mean games like those of PopCap and PlayFirst: you know, Bejeweled and the like. Okay, so first of all, it's a \\(240 million a year industry, projected to go to \\)900M by 2009 (but on the other hand "projected to grow to..." means "someone made up this number").
Greg Canessa, group manager of XBox Live Arcade: "The conversion rates, from free to paid, were staggering. The industry average for PC-downloadable games is under 1 percent, and we were getting a sustained average conversion rate across our 20 titles of almost 12 percent." (emphasis added).
I've been there, I know: Game development is the worst freaking subset of the software development industry you can imagine. But holy cow, with Microsoft's preview of XNA that was just released at the Game Developer's Conference, you can now use C# or VB.NET to write the next Tetris / Bejeweled / PacMan. Man, is that a tempting market. Man. I mean... Man.
And if you don't want to learn DX, PopCap has released the engine they use under a no-fee, Open Source, must-give-credit license.