All the shiny details on whats in it at http://windowsvistablog.com/blogs/windowsvista/pages/windows-vista-service-pack-1-beta-whitepaper.aspx
- DirectX 10.1 support
- Bitlock any drive
- Approx 1Gb in file size!
- New file system support for flash drives (exFat)
- Lots and lots of performance improvements
- Reliability (improved can't really be used here )
All this goodness Q1 2008 (According to the team blog )