It imported my little "other" iTunes Library of about 1,500 songs, albeit with some stalls. However, for my main 20,000 song library it just crashes out.
I hate to say it considering the other feedback, but I'm not a fan of the UI. The giant words instead of icons, off colour and sort of grafted on now playing box, and no ability to hide the "browser" all put me off pretty strongly. Integrated preferences was a bad choice, too IMO. That's a good lazy solution for an app like Chrome to support all platforms, but for a proper OS X app I see no reason to avoid a standard prefs window. Prefs shouldn't be given equal prominence to actual application functions. In fact, because you are using words instead of icons and "Preferences" is such a long word, you are actually giving it greater prominence.
I'm lost as to the purpose of the sidebar. I get that it jumps to the currently playing album, but why can I scroll around to other unrelated albums? It's like there are two completely independent browsing frames in this window. Plus I can delete things in the other frame with the "x" button, but they just go away temporarily until I start playing a song again... I just don't get it.
Honestly, besides startup time, iTunes does everything this does better and it does it with a more refined UI. I know the standard response is "great job! can't wait to see the progress!" but I feel like I need to be honest. There are a million iTunes replacements and companions out there. They all suffer from requiring more effort to manage two music playing apps and offer dubious benefit. They all have small dedicated user bases but they never take the platform by storm like they seem to be hoping to. I'll keep it around as I would like to see if it can handle a 20,000 song library with future updates, but I don't see myself using it over iTunes. Sorry.
EDIT - Before you reply about the draw of features like extended filetype support, last.fm and queuing, consider that almost every iTunes replacement/companion (and there literally are dozens of them) has these features already. That's also a reason to take comments like "Can't stand iTunes bloat, definitely interested!" with a grain of salt. If these people were actually receptive to change, they most likely would have switched to an alternative long ago.