Google will be holding a hackathon on August 24th from 10AM to 5PM, at Google Campus: 1600 Amphitheatre Pkwy, Mountain View, CA 94043, to help you get started integrating with Google Apps and the Google Apps Marketplace! "We'll be doing short introductions and presentations throughout the day on many of the Apps APIs. There'll be plenty of time to try out APIs, ask questions, and get hands-on help from members of the Google team and other local developers. Bring your laptops and come hang out at Google. Food will be provided," informs Google. More Info: Sign Up.
Also, If you're primarily interested in Google Apps Script, Google's having a separate hackathon on September 23rd just for Apps Script. Please see this site for more information.