The unstoppable PostgreSQL team just announced the first release candidate of 9.2, with several bug fixes since the Beta 4. If you haven’t tested 9.2 yet, now is the time! Remember that you can run a copy of your 8.4 or 9.2 cluster in parallel for testing with pg_upgradecluster.
If you use Debian, 9.2rc1 will be available in experimental in a few hours. For Ubuntu, you can get packages for all supported releases from my PostgreSQL backports PPA as usual.
Enjoy!