I don't know if it is worth mentioning but as a Ubuntu 10.04.1 user, I noticed the 8.4.6 update to PostgreSQL was pushed by Ubuntu near the end of December.
http://www.postgresql.org/docs/8.4/static/release-8-4-6.html first item of the release notes mention the database can fail on some file systems notably ext4 with data=journal mount option. I mention it only because your problem appears with the use of postgres.
