I am cofounder of a affiliate/PPC analytics tool that is currently in development. While we aim to incorporate both adwords and adCenter so far this has been limited to adwords because Microsoft have only ever ran an invitation only program for API access (to the best of my knowledge).

While the response we have go is that they will eventually open it up being able to develop for it now would be of great advantage. It seems at this stage only those with large advertising spend are getting keys, we have had an account for some time but have always used adwords more heavily.

Just posting this in the off chance someone that works with this stuff at Microsoft hangs out on HN and can help a startup out :)

Thanks.