Feel free to add new/remove fixed etc.
http://kernelnewbies.org/known_regressions_2623 regressions in 2.6.23
http://kernelnewbies.org/known_regressions_2622 regressions in 2.6.22
http://kernelnewbies.org/known_regressions_2621 regressions in 2.6.21 (unmaintained)
Distro-tracked regressions
Gentoo
This list is kept relatively up-to-date. Gentoo kernels are only lightly patched, and the majority of bugs have been reproduced on unpatched kernels and reported upstream. Gentoo only track release kernels, not -rc releases (it's nice to see the scope of Adrian's previous work increased).