In the comments he says that the restrictions were not THE problem, THE problem was the instability. List of restrictions is kind of reminder of what he had to cope with, and wasted money on, until it turned out that GAE doesn't work properly.
You can use all kinds of techniques to protect your application from things like variable datastore performance. For example, nowdays I usually use a pattern where user-facing servlets only ever read from the datastore - all updates go via a taskqueue, which means that even if the datastore is in maintenance mode the updates will eventually be applied.
GAE isn't for everyone, but the first step to getting the most out of it is accepting it isn't anything like a typical frontend plus database architecture.
We (http://gri.pe) are still happy on AppEngine, even though September was rough.
But it does appear to be fixed now.
Unless the platform scales as it should, which is the whole point of accepting all the limitations. If there are tight and hard limits on request timeout, then there must be equally stringent guarantees provided by the underlying platform. "We're working on it" is just not enough under these conditions.