You expect to find Java apps on Mac OS X which don't leverage the cross-platform angle? Crashplan is the best Java app I use on the Mac, and the Mac is a big part of their business. Apple itself uses them, from what I understand.
Part of what makes CrashPlan so killer is that it's not cloud-centric. It also offers backups to local storage, backups over the internet to authorized peers, and in the pro version, centralized backups to one's own servers and storage, which is obviously what Apple uses.
Check it out. It's the only offsite backup utility I know of which not only covers all the bandwidth conservation bases (compression, data de-duplication, block-level updates), but also allows you to do an initial backup to local storage, ship or transport the disk, and then continue to back up to it over the internet.
And before some intrepid nerd starts waxing rhapsodic about rsync and tin cans joined with string, CrashPlan also offers a respectable UI, sensible default backup selection, end-to-end encryption, firewall traversal, email notifications, total OS agnosticism, and a free version with all of the above.
Hell of a product. I have no relationship to the company except that of a satisfied customer.
We sell our server hardware as well, so clients can have their own backup cloud. Most of our very largest clients (who shall remain nameless) use this approach.
http://twitter.com/crashplan/status/28403694811
(Alas, linebreaks stripped by the website.)