I'm on 5353 which is really stable - so much so I've moved to it for my production system. Having said that the official advice remains "this is a test build and therefore shouldn't be relied upon in production". I like living on "the bleading edge of technology" so I'll take my chances.
Doug cites 5381 as being equally stable.
Once you've tried a stable build of Windows Vista it's hard to go back to Windows XP