Here's one obvious use case: social apps. Most apps on facebook, myspace, etc don't really require perfectly normalized data, most of the stuff is just for fun

Here's one obvious use case: social apps. Most apps on facebook, myspace, etc don't really require perfectly normalized data, most of the stuff is just for fun, or games to generate ad revenue etc. Plus, you don't have to worry much about the scalability issue other than making your queries run fast, once it's on app engine, a million myspace users hitting your app won't even make you worry. I've got my own colocation facility with virtual machines and the like as well as an amazon ec2 account with several vms, but I still make use of google app engine any time I want to write a facebook/orkut/myspace app.