Yeah I'd like to know more about that too. Having just switched from PC (boo!) to a zippy-flash, it-don't-crash iMac, I am forever thinking I need to use an UnInstaller to eliminate a program...and if I don't, that I'm leaving behind a bunch of tendrils and tentacles from the banished program.
Does just plunking it into the trash do the trick - then when I restart OSX does it clean itself of unnecessary files and things?