I should say, even before I start this post, that I've moved my iTunes library from one installation of iTunes to another, and what I did was just copy everything in the /Music/iTunes folder from one Mac to the other. But that's the transfer equivalent of parallel parking a semi and stopping when it "feels right" -- it worked for me, but I wouldn't recommend it for anyone else. I also have almost no iTunes purchased music in my library, and that's likely not the case for anyone else.
Fortunately, for people who don't enjoy playing Russian Roulette with their iTunes library transfers (and don't want to buy the software for it), here's a quick and easy guide to how to transfer everything over properly, and make sure that all the little hooks and crannies line up correctly in the new installation -- specifically, iTunes keeps an XML file that tracks where everything is, and you've got to change paths (using a quick find and replace) on all the tracks in your library. iTunes will then use that XML file to backup its own records, and then you're hunky dory.
What I can't find, according to this guide, is what damage I may have caused to my system by just hauling everything in and starting up iTunes -- I checked the Location key on both my new Mac and the old one, and the Locations are completely different, without me ever changing them. Either way, even though I throw around my libraries with abandon (look Ma, no backup!), you'd probably much rather be safe than sorry.