Some of What's New In This Version (from the User Guide):
Performance improvements: The speed of all import operations has been improved on Macs with PowerPC processors. Subclip importing is also faster in this version of the software, on both PowerPC and Intel-based Macs.
New video codecs: The new Apple video codecs included in Final Cut Pro 5.1.2 are supported for import and export (actually this is true of XDCAM Transfer V1.0 as well if you've got the right version of FCP). Final Cut Pro now supports XDCAM HD (18 and 35 Mb/s VBR) at all frame rates. HDV (25 Mb/s CBR) is supported at 25p as well as at 50i, 60i and 24p.
Essence Marks and additional workflow enhancements: Essence Marks now appear in the XDCAM Transfer clip player on the timeline as well as in an overlay on the video image when the playhead is positioned at the Essence Mark. When clips are imported directly to Final Cut Pro, the Essence Marks become clip markers in Final Cut Pro.
Import now also transfers more metadata to Final Cut Pro, including the source disc or folder name and the clip comment as the 'Reel' and 'Log Note' respectively. There is also a new Preferences option to only import the monitored audio channels. Shortcuts are now provided for Import All Clips and Import All Subclips. The subclip lists are now saved when the application quits to enable offline subclip selection for later import.
There are some other bits of new UI like resizable thumbnails, snapping in the timeline, more feedback in the Activity window etc. to play with too.