The AngelList API recently hit 3 million requests a day including:
Big VC firms who shall go nameless are using it too (we haven’t asked their permission to mention them by name).
Developers around the world are using the API to create iPhone and Android apps, visualize the world of fundraising, and automate their startups’ AngelList profiles. See a few of them here.
The API began as a side project by Josh Slayton; the first big customer was Rapportive, who still sends nearly a million requests a day to the API.