For many people in OS X 10.2, Chimera will not stick as the default web browser in the Internet System Prefs. There have been many suggestions as to how to make it stick (three hints here - 1, 2, 3), but only one that I thought of seems to work for anyone who has tried, and has survived logouts and reboots.
Doing this takes only one step in Terminal. Simply rename the file /System -> Library -> PreferencePanes -> Internet.prefPane -> Contents -> Resources -> English.lproj -> DefaultHelperApps.plist to something else, so for all intents and purposes the file does not exist to the OS. I named it DefaultHelperApps.plist.10.2 to easily remember, in case I need it back. Simply quitting System Prefs then starting them again should be all you need to do to make it take effect, but logging out and then back in never hurts.
Alternatively, you can get to this file through the GUI by going to /System -> Library -> PreferencePanes and then control clicking on Internet.prefPane and clicking Show Package Contents. Then go to Contents -> Resources, then your language's .lproj, and then rename the file.
This "fix" should also work in 10.1, but I'm not positive. Good luck and happy browsing!
[Editor's note: I haven't tried this myself yet, but it shouldn't have too many negative consequences. The file is used to set the default values in the preferences panel, but it doesn't affect your ability to choose a setting in the Internet preferences panel.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020916060831754