I haven't checked it out, but my experience with java apps is that they're generally pretty much on the heavy side, and the GUIs are laggy and klumzy. I suppose for a backup tool, though, the running speed shouldn't be too bad, since you're going to be file I/O bound. Guess it's worth giving it a shot.
PS: yes, I'm biased - I dislike java programs even more than I dislike dotNET programs. Probably wouldn't be so bad if the ms<>sun case hadn't happened, and we still had the faster&lighter MS JVM.