Hi,
I participated in the Amgen Scholars program at UCSD this past summer. It was a very fun experience--possibly one of my best summers, but not necessarily because of the Amgen program--and I would highly suggest it for anyone who's interested. Plus, the pay is great too. We got $3.5k at UCSD plus a board stipend of $700, including free living on campus (own room), 4 units of school credit, and an awesome trip to Lake Tahoe over the summer.
I also got to know a wonderful PI who I still talk to regularly and will be presenting my summer research project at a National Conference in TX next week (all expense paid trip, to boot--not sponsored/paid for by Amgen).
Results will vary. But I think you'll enjoy it greatly =)
Hope this helps. Good luck.