You got it backwards - the smart user NEVER lets Software Update muck things up. Always wait a week after announcement and check Macintouch and MacFixIt to see how may people are having problems. The bugs in Mail app became apparent with 10.5.5 and got no better in 10.5.6 so you're better off staying at 10.5.4, which is the version that comes on the latest MacBookPros.
You'd be amazed at the number of MBPs that show up at the Linux Users Group meetings, oh trollers.
I think Apple has been hiring dropouts from the Bush administration to write their updates - they are consistently of the Heckuva Job Brownie class. The last good Safari was 3.1.2 and it still is dog slow compared to Camino. The Security Updates spray fecal firehoses all over anyone who is misfortunate enough to run them. Too bad, because there are some security holes that need fixing. And don't get me started on QuickTime 7.5.5 or iTunes 8.0.x.
Eventually someone will clean up the mess, but my guess is that will happen with 10.6.3.
I would still rather have my eyes chewed out by eels than run Windows of any stripe. If Apple died tomorrow I would install Ubuntu.