Is anyone using PostgreSQL 9 and mediawiki in a production environment? Anything to watch out for? Thanks!

I'm not using it anywhere yet in production, but it's heavily tested on 8.4 and should be fine, as nothing radical has changed between the versions. And for better or for worse, it's not like MediaWiki really takes advantage of some of PGs strengths, so the interface is kept pretty simple, which means it's a rare day indeed when a new version of Postgres will not work against MediaWiki. If you do see anything, raise a bug of course!