Bug in newest version of GAE you can save but when you load it crashes.
The 'newest version' of GAE is 0.3.2, and save games work fine.
If you are using a build from trunk, then you may experience any number of problems. While most of those problems will be fixed immediately after they are noticed, that is unfortunately not likely in this case because,
A) Save-games will just be broken again later, especially whilst refactoring work is ongoing
and,
B) All of the serialisation code is being replaced in the near future anyway, so any fix applied now would just be wasted effort.