Here is a couple of Windows 7 KB that might be of interest to HTPC users:
Unexpectedly slow startup in Windows 7 or in Windows Server 2008 R2
A Windows 7-based computer that is equipped with a hybrid television tuner does not enter sleep mode
FIX: MPEG-2 transport streams or certain variable bit rate WMV files may not play in Windows Media Player on a computer that is running Windows 7 or Windows Server 2008 R2
Over time I saw a few updates that could help improve performance of HTPC systems. If you find anything important, please post here.