I have a distinct bias towards Java apps because they're usually slow, ugly, non-Mac-like, etc., but this was a pleasant surprise.
While there are certain column list behaviors and other bits and bobs that annoyed me, such as the peculiarly basic and vastly unMac file dialog and the very unMac... kinda ugly "toolbar" icons, in most ways that really count it does it's job more than adequately.
It scanned one of my larger, more cluttered drives very quickly, and I must admit JDR's simple sorting, graphing and statistic functions and displays are nice. It has a surprisingly rich set of prefs.
While the appearance themes technically aren't terribly important, they're a great idea for a cross-platform app, and i'm sure had i been forced to look at icons and heirarchical lists that looked like windoze, i'd have torn into the app on that account.
I own DaisyDisk and I suppose i'll be sticking with it's OS X flash, but this unique little FREE app is impressive.