Here is a list of some of new features being introduced in SL5 from ScotGu's blog.
- Hardware video decode
- Trickplay
- Remote control support
- Better Databinding and MVVM
- WCF and RIA Services: Silverlight 5 now includes WS-Trust support.
- Improved text clarity
- Better printing support
- Out of browser support
- Better and faster drawing
- Automated testing tools
- Smaller download
- Faster performance
Watch ScotGu's keynote here