App Engine and Java
The world is now split into Python programmers, making funny 'Goo' noises over App Engine, and everyone else who are wondering when/if this will be available in their language or if they are going to have to change their spots.
Of all the languages to support, I guess Java must be one of the hardest because of the heavyweight runtime and the difficulty in separating code. But it also makes sense because supporting Java might give you quick access to Ruby/JavaScript/etc.
I have no knowledge of if Google are going to support Java in App Engine, however there are some tea-leaves that can be stretched and rearranged to form a vague picture.
Some time ago Google hired Greg Czajkowski the lead of Project Barcelona from Sun. Project Barcelona was where Isolates (JSR-121) came from and the Resource Consumption API (JSR 284), both of which would help you do this sort of thing. And both of which are now in Final Draft stage.
I have no idea if this does mean that Google are working on App Engine for Java, but if they do I'm going to claim bragging rights for having blogged about this 18 months ago.
Re: App Engine and Java
And, say compared to PHP, Java already offers a bunch of packaging and deployment options. I'm sure they figure something out.
In any case I think App Engine provides the missing piece to the big Google puzzle, answering the "Whats their revenue in a few years, when AdWords don't grow anymore?". And it nicely brings all the existing pieces together.