Are you running Windows 7 via Bootcamp or a VM? I was wondering if a VM was powerful enough to handle DVR tasks.
I'm using bootcamp. The only time I boot into OS X with it is to apply EFI updates. The mac mini's sole job is to be a media box which runs two HDHomeRun tuner units (4 tuners total), play 720p/1080p mkv files, and run an FTP server in the background. Occasionally, I'll use it to encode/transcode movies.
I have the concurrent user hack installed so whenever I need to perform any maintenance tasks, I just remote in with a different user account.
For mkv files, I'm using CoreAVC paired with combined community pack to take care of the audio pass-through (S/PDIF out).
Attached to the mac mini are two external USB 2.0 drives (a MyBook raid-0 2TB drive and a MyBook 750GB drive).
The CPU usage is between 10-20% when watching live TV or playing 1080p mkv files. CPU usage jumps a tiny bit when recording 4 simultaneous TV shows. The temperature doesn't go above 65C in most cases.
I have a Logitech Harmony remote configured to turn on the TV, receiver, and launch MCE whenever I push the "Watch TV" activity button. When I hit the power button on the remote, it turns off the TV, receiver, and then quits the MCE application.
I had to set some special events for the mac mini as a device in the Logitech remote profile because I'm using a miniDP to HDMI adapter for the TV. Whenever the TV turns on, there's a delay of about 10 seconds before the mac mini will detect it. If the MCE app is launched before that, it'll display in 1024 x 768 until you quit the app and re-open it. I set the remote to "open" the MCE app (in actuality, it's only hitting the OK button 2 times). Once all of the devices are turned on, it waits 10 seconds and then launches the MCE app.