After 20 days of final polishing and maturing since the release candidate, the PostgreSQL team released the final 9.0 version today.
Hot off the press, I uploaded
postgresql-9.0 final into Debian unstable; they will not go into Debian Squeeze, because Squeeze is frozen and it will take a long time to port all the packaged server side extensions to 9.0.
If you are on Ubuntu 10.04 LTS or Ubuntu 10.10, you can add my PostgreSQL backports for stable Ubuntu releases PPA, which will carry 9.0 until it can be moved to the official Ubuntu backports (i. e. when 9.0 goes into Ubuntu Natty).
Enjoy, and kudos to the PostgreSQL team!