Where is the preference file? The pref pane has gone all unresponsive and I can't alter what Unarchiver should handle. I reinstalled but my selection stayed so somewhere there is a file. Thanks. Oh, by the way, great job. Stuff-it always seemed like it was on the verge of crashing. Funny thing, I was testing relative speeds between your app and stuff-it and stuff-it just crashed on the archive. Ha Ha. I knew it sucked but it hadn't really crashed in a while. My decision was made.
The associations aren't stored in a preferences file, but the previous ones are, and there's a bug where those get corrupted, so that might be your problem. It should be at ~/Library/Preferences/cx.c3.xee.plist.
Just drag it where you want it, usually the Applications folder. This is how you normally install program on OS X.