It's great. I use it mostly for small projects and weird prototyping ideas (http://wookietranslator.com). It does take a while to configure and get going (unlike Heroku) but Google has good documentation for Python.

Nothing, but there was a steep price increase when App Engine went "out of beta". This upset some people. Especially because there is a lock-in effect if you build on top of App Engine's proprietary APIs.

Snapchat runs on GAE so it must not be too bad.

http://blog.snapchat.com/

Take a look at the issues page for many of the top requests[1] as well as the included libraries for Python.[2] There are requests for python3 support, but also for pandas, scipy, etc.

GCE should be more flexible since it is providing infrastructure rather than the platform. However, depending on your project getting an entire platform from Google first could save you effort.

[1] http://code.google.com/p/googleappengine/issues/list?cursor=...

[2] https://developers.google.com/appengine/docs/python/tools/li...