Many announcements and blog posts regarding UR2 for MCE have been published during the last few days. But for me as a developer the most interesting change I've discovered in Michael Creasy's Update Rollup 2 for WIndows XP Media Center Edition is live!:
.NET Framework 1.1 support Media Center now uses version 1.1 of the .NET Framework. Add-ins can now be built using 1.1, but 1.0 addins will still work.