Although an old article, it's still probably the best reference for Google's Feed APIs out there. I considered using the APIs some time ago for a project in which I need to pull tens of thousands of feeds, but Google's TOS limit it's use to not-for-profit projects. I ended up using the SimplePie PHP library, and I'm very happy with it.

Thanks for posting this. I know it's three-ish years old now, but I still hadn't heard of it.

Man! I got all excited. This is the same post I found years ago ;)