I, and a number of my friends, have notied that certain features in Quicksilver seem to be disabled for 10.6 users -- features such as the preferences pane. Going to the Blacktree web site and downloading the B56a7 version seems to fix most of the problems for us, though at the expense of more crashes. And unless you've attempted to access any of the problem spots, you may not have noticed the problems.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090930094402448