I was one of the lucky few to get an account in the first round of AppEngine signups, and today I started in on my first app.
I recently found Edward O'Connor's backpackit entry on Personal Unit Tests, and I thought this would make a great little app to get started with. It's like a daily goals tracker, but with a very slightly different focus. More on that tomorrow.
Overall, I was very impressed with the amount of minor annoyances google has removed with this new setup. Having worked with these types of webapps for a number of years now, I know that they're rarely easy to host and deploy, but google has certainly taken the grunt work out of the equation.
I was most impressed on the user account tie-in they've built. It's absolutely trivial to let people use their own google accounts [gmail accounts] instead of creating a new account on each site. Effectively, they've built their own OpenID implementation into the framework.
At the end of the day, I'm reminded a bit of GeoCities and Tripod, who brought static webpages to the unwashed masses. With AppEngine, all that's needed for a small app is a handful of yaml, some html, and a few hundred lines of python.