Probably the most amusing, to me at least, comment after the AppEngine talks yesterday was "It's all about concurrency."
The thing with AppEngine is that it is factored in such a way as to allow insane amounts of concurrency in a way that doesn't break programmer's heads. The traditional programming by mutation based computation model is still present. There is no need for programmers to get side affect free religion to use AppEngine's massive scale out capacity.
The only downside of AppEngine is that it requires programmers to grok DataStore. DataStore is where the concurrency rubber hits the road, and it breaks programmers. Programmers are control freaks by nature, and being forced to give up control for MT safety is emotionally hard.
It's going to be an interesting decade. Just as the wide spread adoption of GUIs forced OOP on a generation of programmers, Multicores are going to force concurrency on this generation. I'm kinda expecting a lot of programmers not to make the transition...