Acocrding to this, the beta version of the iPhone SDK has been downloaded over 100,000 times since it was launched last week.
In addition, both Namco and PopCap have pledge support for the platform with Bejeweled, Zuma, Peggle, Pac-Man and Galaga all confirmed for release.
Still no idea when you're actually going to be able to use the App Store on iTunes and actually play any of this. Quite exciting though, isn't it? Apart from the Peggle bit, obviously.