I'm pretty sure that the greatest "wow" factor of MM is the Amazon tagging. I can't tell you how important that is to me. Sure, there are other apps that tag, and even other music managers that claim this functionality with mixed results. Let me tell you...my life might be a mess sometimes, but my music is tight. MM's integrated tagging makes this sooooooo easy. And it all comes down to the all-in-one-place coolness - I can tag and everything else while still in the same app, without the need for a gazillion different programs, each with their own navigation, appearance, and taskbar entry to get on my nerves.
MM was the first manager that allowed me to ditch all of my ancillary, single-purpose music apps. For the longest time I was running iTunes soley to sync (the abject misery of using it as a player is well-documented). Then I ran another app for accurate tagging and art; yet another that acted as a non-intrusive, nimble player of files, and still another for audio-related burns, etc. Enter the Monkey.
Right away I could tell that I was, well, home. The free Monkey did most of the above tasks. Paying the nominal fee ensured that I never, ever have to roam anywhere else, even if it's to burn a particularly good playlist that's rolling along. Now, only two other music-related apps reside on my computer. iTunes...still...because I'm pretty sure that I need it in the rare event of a setup (act as disk, etc), and mp3gain, which I use to normalize files across genres and recording technology. But the Monkey is always running. The only thing experiencing as much up-time is my browser.
I'm excited that I can customize MM as I see fit, from my tree to my panels, etc. Only Foobar is more tinker-worthy, but correspondingly more irritating. I also love the community, which I've thankfully seldom had the case to use. But it's there should anyone need it, full of polite, knowledgeable peeps. MM has only gone sideways on me once, which was resolved with an reinstall and not too much sweating it.
I campaign for MediaMonkey whenever a casual discussion about digital music is brought up. Almost invariably I'm thanked for the tip. And now I'd like to thank the people who officially work for MM and all the community members who make this the ONLY piece of software I've ever gushed about in a forum.
PS - MM is also the main reason I can't convert to Linux full-time. Can't get it running smoothly in Wine. If one app is more or less the deal-breaker in your OS choice, well, that's one heck of a compliment!