Looks like Microsoft quietly released Silverlight 5 back in December. It has yet to appear in Windows Update, but can be downloaded here:
http://www.microsoft.com/getsilverlight/get-started/install/default.aspx
(A reboot is necessary after installation or you will get DRM errors with protected content.)
I have two initial impressions on my Core i5 2500K/Intel HD Graphics 3000/Win 7 64-bit HTPC:
First, the judder with WMC Netflix streaming is finally gone; HD content is finally enjoyable to watch. But since the Netflix app hasn’t been updated in a very long time, still no subtitles or 5.1 sound for certain movies.
Secondly, Live TV starts up much faster with the PCIe Ceton InfiniTV 4 when resuming from sleep. This is a welcome change – no more staring at the “Viewing or Listening Conflict” message for what feels like an eternity.