Sure Google Appengine scales, but is it also fast?

I want to know if responsetimes are good, not just if it scales. Anyone with experiences?

From stackoverflow

• A scalable architecture like GAE is not the same as one based on optimizing speed. A different approach is needed.

  The DataStore isn't designed to be super fast at the small scale, but rather handle large amounts of data, and be distributed. We could say that database access is "very slow" at the small scale (compared with a standard relational database).

  Take a look at: google-appengine-second-look and how-i-learned-stop-worrying-and-love-using-lot-disk-space-scale

  Some experimental results.

  Eric W. : To clarify the above points, the GAE datastore has been optimized first for scalability and after that for reads. Writes are slow, but it turns out that queries and gets are pretty fast, in practical terms.
  From Guido

• I've implemented some ajax popups for a GAE application and the popups need a server round trip to be less than half second on average to be usable. And it turned out to work pretty well. The support for memcache also makes it easy to optimize for speed on GAE.

  From Jiayao Yu