I'm using SQLgrey 1.7.4 on FreeBSD 6.2 with PostgreSQL 8.2. I was also having it with FreeBSD 6.1 and PostgreSQL 8.0 before the newer (fresh) setup.
The "Postgres" process continually grows in size slowly over time. Restarting SQLgrey fixes this - but it needs to be done pretty much every day.
I googled around for quite some time about this issue - I see there's at least one other person with it. "Andrew Diederich" is also having problems - not sure if he's using FBSD but he's using PGSql+SQLgrey.
There were some remarks on the forums about replacing "prepare_cached" with just "prepare" - I've tried this to no avail.