Our son’s housemate had an idea that seemed to have considerable merit, involving an application and a website that allows the users to coordinate activities and communicate with each other.
For the back end, it seems that Google AppEngine is a good choice. My biggest concern with it right now is that it is a preview release at this time. I don’t know how long before they release the limits to allow applications full performance. Because of that, I’m tempted to consider another alternative, like maybe Amazon Web Services, since they don’t have these restrictions. The major advantage that Google adds is the theoretical ability to scale to large sizes seamlessly. The downside, they are capping that possibility at this time, with no indication when that may change. It would be a bummer to build a system to take advantage of the scaling, and then have it shut down just when you’re building momentum.