We've had a good 10.5.7 update experience (loads of snappiness™!) on our machines but the Internet is filling up with issues related to the massive install. MaxFixit goes over the major problems and the workarounds as per usual.
A good rule of thumb on this one is run a permissions repair before upgrading and the Combo updater seems a little safer.
For Blue Screens:
Don't use Software Update. Instead, download the standalone "Combo" updater.
Reboot into
