Jade,
AFAIK HEAD doesn't requite PG 7.3. I'm running the test server on PG 7.2.2 and I don't know that this has caused any problems.
I mostly worry about all the brokenness in .LRN that is obvious if you browse the test servers a little. Calendar is still broken and I am talking to Dirk about a resolution. Quite a few bugs seem related to I18N and noquote and feature quite prominently in the UI. Hopefully they will mostly be trivial fixes.