The Python 2.7 transition
We want Python 2.7 as the default Python 2 version in Wheezy. It may be the only Python 2 version. In the meantime, Ubuntu Natty (11.04) has enabled Python 2.7 as default version, while Python 2.6 is still supported. The general plan going forward is to fix Python 2.7 compatibility issues in experimental (until Squeeze is released) and then sync them back to Ubuntu.
Here is the start of an email thread that discusses the transition plan.
The definitive, comprehensive resource on changes in Python 2.7 are in the What's New document. Most of those changes will not affect packages that are already compatible with Python 2.6. Here are the list of things that you need to watch for when updating a package to be Python 2.7 compatible:
The Fedora project is well on their way to Python 2.7 compatibility, so with proper attribution we can utilize their patches when necessary. They've been diligent (as we should be) in submitting their changes upstream, so in many cases we might just need to update our packages to the latest upstream.
Tips and tricks
If you care only about byte-compilation, installing a package is overkill. It's way easier and faster just to unpack the .deb (dpkg-deb -x) and run python2.7 -m compileall /path/to/unpacked/stuff. (Given by Jakub Wilk)