If you find StuffIt v10 is crashing when launched under Tiger, try this.
Open the Network panel in System Preferences, and set IPv6 to Automatic on your active network interface (via the Configure IPv6 pop-up). You can then disable "Allow Version Checking" in StuffIt, and disable IPv6 again. A future update to StuffIt should fix this problem...
[robg adds: I can't confirm the problem or the solution. If you can comment one way or the other, please do so...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20051106073435181