Subsequent to the changes introduced by the new Foxy Fixtures feature in Rails 2.0, the PostgreSQL adapter functionally requires PostgreSQL 8.1 or better. Prior to 8.1, there was no support for the DISABLE / ENABLE TRIGGER action for the ALTER TABLE statement.
So if you're getting this big, ugly error (or similar):
PGError: ERROR: syntax error at or near "ENABLE" at character 25
when running your specs or tests after upgrading to the latest release candidate, that's what's going on. Doing an upgrade to 8.2.5 solved the problem for me.