Changes since the previous version (1.50a) include:
New User Interface
New first-time setup wizard
New configuration dialog
New backup preview dialog
New backup selection dialog
Support for new Jungle Disk 2.0 buckets
Instantly rename files and directories
Optionally encrypt file & directory names
Change encryption key (bucket password) for existing files instantly
Unlimited number of buckets supported
Support for Compatibility buckets, which can be shared with other S3 tools
Support for European S3 buckets (note: Jungle Disk Plus not supported)
Support for connecting to multiple buckets at the same time
Support for multiple backup jobs with independent scheduling
Expanded bandwidth limiting feature
Applies to both network drive and automatic backup traffic
Set limits on both upload and download rates
Change limits on the fly
Set schedules for limits
New Previous Versions features
Set minimum and maximum number of previous versions to keep
Exclude file types and directories from previous versions
Customize previous version settings on a per-backup-job basis
New command line options to integrate with external task schedulers and batch jobs
Greatly improved performance for large directories and large cache sizes
Tray icon changes to indicate errors occuring
Buckets (and their data) can now be deleted from configuration dialog
Verify MD5 hash on downloads (as well as upload)
Fixed highlight color in Mac errors & warnings list
Fixed crash when backing up directories with large numbers of sub-directories

Leopard 10.5.3 compatibility

http://www.jungledisk.com/relnotes/relnotes.shtml