PostgreSQL recently published new point releases which fix the usual range of important bugs (data loss/wrong results, etc.) and additionally fix another case of insecure “security definer” functions (the analogon to setuid programs in file system space for SQL functions) (CVE-2007-6600). Please see the complete changes for 8.1.18 (Ubuntu 6.06 LTS), 8.3.8 (Ubuntu 8.04 LTS, 8.10, and 9.04), and 8.4.1 (Ubuntu 9.10).
8.4.1 is already in Ubuntu 9.10 and in my PostgreSQL Backports PPA for Ubuntu 8.04 LTS and 9.04. Updates for the other supported Ubuntu releases are currently in -proposed, waiting for testing feedback.
If you use PostgreSQL, please give the -proposed packages some testing and report back in Ubuntu bug #430544. Thanks!