Apple has dropped a 10.5.2 update out on Software Update. The patch has a number of different bugfixes all across the OS, from Dashboard and Airport improvements all the way to a menubar option in Time Machine and the disabling of GrowlMail 1.1.2 or earlier "to avoid security issues fix 1.1.2 from crashing growlmail."
My Software Update is apparently taking its sweet time downloading the patch, but other TUAWers have already grabbed it and gotten rolling. Welcome to 10.5.2!
UPDATE: Chris Forsythe from Growl notified us that it wasn't a security issue with Growl.