I was unaware of this, thanks for bringing it to our attention.
As far as the function problem goes, PG 7.3 will have a "CREATE OR REPLACE" function capability that will fix that problem (for those of you wondering why Oracle has that construct, it's to avoid the very same problem).
We should dig into the constraints issue more deeply. Any volunteers? Dropping the table will also kill any audit history you've built up before installing ETP which doesn't sound very cool to me...
