If you're currently running any 7.1 beta release, and you want to update
to 7.1beta6 (or later) without doing an initdb, you *MUST* run the
contrib utility contrib/pg_resetxlog after shutting down your old
postmaster. This will update your pg_control and XLOG files to their
new formats. See the README in that directory for detailed instructions.
If you get a complaint about incorrect PG_CONTROL_VERSION when you try
to start the new software, you forgot this step.
Please note that there was a nasty bug lurking in version 1.1 of
pg_resetxlog; it's fixed in 1.2 committed last night. Don't use 1.1
(or if you already did, I recommend a dump/initdb/reload before you hit
problems).
regards, tom lane