"Although Python is currently the only language supported by Google App Engine, we look forward to supporting more languages in the future."
You see, Python is their first choice as the main language for Google App Engine. It's not that surprising, Google is known to be a Python company. I'm pretty sure that Java, .Net and Ruby support will be available very soon as well. I wonder when will be the first time that some of the Google (or other companies) services are available only with dynamic languages.
What is my point here?
If you are serious about your career in IT then you have to start learning how to develop software with dynamic languages.
Python or Ruby seem to be good candidates. If you ask me - if you come from .NET world go for IronPython, if you come from Java choose JRuby. That's a good start. Good luck!