While nothing security related is specifically mentioned (AFAICT), potential data-loss conditions have been fixed. IMO, data-loss is as bad as insecurity. Here's part of the official announcement dated 2008-09-21:
Updates for all maintained versions of PostgreSQL are available today: 8.3.4, 8.2.10, 8.1.14, 8.0.18 and 7.4.22. These releases fix more than thirty minor issues reported and patched over the last three months. As some of these issues carry a risk of data loss, administrators of production applications should upgrade in their next possible scheduled downtime.
Additionally, this minor release also contains updates for the following timezones to support changes in local laws: Argentina, Bahamas, Brazil, Mauritius, Morocco, Pakistan, Palestine, and Paraguay. Users in these timezones should plan to upgrade as soon as possible to avoid improper calculation of daylight savings time.
Issues fixed include autovacuum crashes reported by several users, two Heap Only Tuple bugs, a foriegn key failure condition, a too-small lock address space, two Write Ahead Log bugs, several planner mistakes, and numerous "corner condition" bugs.
EDIT: I have been the PostgreSQL packager so far, but have fallen way behind due to lack of time. Mostly I have yet to adapt my packaging script to the official VL format, so if anyone can help, let me know and I'll send them the script as it stands.