Another datapoint:

For Fedora 16, I haven't done any downstream patching (so far), because we hadn't run into any downstream problems.

I did some digging into why we're _not_ experiencing issues.

Currently for Fedora 16, we're shipping kernel-3.0 with python-2.7.2-4.fc16.x86_64 and python is reporting:

  $ python -c"import sys; print(sys.platform)"
  linux2

I investigated why we have this discrepancy:  "uname" with the build environment for that RPM happens to be reporting a kernel-2*, whereas we're shipping a kernel-3*:

  http://koji.fedoraproject.org/koji/taskinfo?taskID=3187563

What's happening here is that although the chroot that the build was done in [1] has:
  kernel-3.0-0.rc6.git0.1.fc16.x86_64.rpm

running "uname" in the chroot environment is reporting the kernel that's actually running, outside the chroot, which was:
  2.6.32
and thus we have:
  checking MACHDEP... linux2
within the build log [2]

So in this case, "sys.platform"'s final digit is reporting the major release of the kernel running outside the chroot-ed build environment (ironically bearing even less relationship to that of the currently-running kernel :( )

Hope this is helpful

[1] http://koji.fedoraproject.org/koji/rpmlist?buildrootID=1096117%20&start=50&order=nvr&type=component
[2] http://kojipkgs.fedoraproject.org/packages/python/2.7.2/4.fc16/data/logs/x86_64/build.log