Google App Engine shows notice to Upgrade Python to 2.7
Here's the deal. 
You have to migrate. They have announced the deprecation of the Python 2.5 runtime and will continue to support it in accordance with the Google App Engine Terms of Service. Here is the section you should concern yourself with...

7.3 Deprecation Policy.
Google will announce if we intend to discontinue or make backwards
  incompatible changes to this API or Service. We will use commercially
  reasonable efforts to continue to operate that Service without these
  changes until the later of: (i) one year after the announcement or
  (ii) April 20, 2015, unless (as Google determines in its reasonable
  good faith judgment):
required by law or third party relationship (including if there is a
  change in applicable law or relationship), or doing so could create a
  security risk or substantial economic or material technical burden
  (the above policy, the "Deprecation Policy"). This Deprecation Policy
  doesn't apply to versions, features, and functionality labeled as
  "experimental."

By my reckoning you have until some time in 2014 until they flat out drop support. 
In the meantime... 
Fork your application. Update the app.yaml to specify the Python27 runtime and for good measure turn thread safety on (you might save some money). 
Test your application. 
Move on with your life.
I hope this posting is in the right location. 
I am very new to Google App Engine, in fact its part of a iOS Application that I purchased from another developer, so bear with me please.
The iOS Application currently has 20,000 active users.  There is no way I can break the system and their Application...so my question is, Should I Migrate to Pythion 2.7 since the message says 2.5 will soon be deprecated.  Does that mean my users will drop if I dont migrate?
If I do Migrate, is there a chance that something might break and completely destroy the userbase and their use to the Application?  What can go wrong if I Migrate?
This is the message at the top of my Dashboard on Google App Engine

A version of this application is using the Python 2.5 runtime, which is deprecated!
The application should be updated to the Python 2.7 runtime as soon as possible, which offers performance improvements and many new features. Learn how simple it is to migrate your application to Python 2.7.
Thanks everyone..
DC