Although it's been relatively quiet in the mailbox over the past 48 hours with regard to Mac OS X 10.6.3 issues and outcomes (probably because everyone is too busy refreshing their delivery status), every OS update comes with a few problems. In this case, the reports we've gotten include the usual mix of stalls, slow reboots, and even one very unhappy graphics card.
Fortunately, the team at cnet's MacFixit site has a solid list of seven recommendations for managing a hung update process, including using the Combo updater and going to safe boot if necessary. If you have been having issues with the update and need a quick fix, run through their list and see if you can't get it working. Oh, and we'll add one more tip, just in case: be sure before you start that your backups are current. Good luck!