It's here ! The most awaited feature is here. Now we have cron in GAE. It's a big day !

A cron job will invoke a URL at a given time of day. A URL invoked by cron is subject to the same limits and quotas as a normal HTTP request, including the request time limit.

An application can have up to 20 scheduled tasks.

And better, it was done like in my dream ;-)

Btw, GAE is one year old (happy birthday !), and is now java compliant.