This is huge for allowing corps to migrate apps onto Google's cloud. Many open source web frameworks can be used on GAE (albeit with limitations), but de-SQLing an existing app is probably a non-starter for most corporate dev groups. Even if scale-up is an issue past some threshold, the long tail of most mid-sized companies' in-house apps includes a bunch of semi-legacy ones which don't have very high usage levels. Think about stuff like the environmental regulation compliance database -- important, but probably not used by more than 10's of people.