Here's an extract from launchpad.net bug 480144:
SRU Justification/Impact: The upstream process for stable tree updates is quite similar in scope to the Ubuntu SRU process, e.g., each patch has to demonstrably fix a bug, and each patch is vetted by upstream by originating either directly from Linus' tree or in a minimally backported form of that patch. The 2.6.31.6 upstream stable patch set is now available. It should be included in the Ubuntu kernel as well.The full list of changes for 2.6.31-17 can be found at linux package log. As you can see, there are lots of drivers fixes and a few security patches.
