I'm in troubleshooting mode now. The last two mornings I've woken up to a frozen server machine. No blue screen. Just the screen contents from whenever it froze some number of hours ago.
I've checked all the event logs and don't see any suspicious activity any time near the freeze. I also had the foresight to leave both Task Manager, PerfMon and the WHS servers running and visible. Nothing out of the ordinary there either.
In both cases a backup from my Vista box was in progress. However, this morning (after rebooting) I initiated a manual backup which just completed successfully.
I do have some processor/motherboard monitoring software running. I'll try pulling that first to see if that helps.
To test out the I/O throughput, I copied ~100GB of video from my Vista box to the WHS machine. Sustained throughput was around 22 MB/second. Both machines have GB LAN cards and SATA II disks. Watching the network throughput in Task Manager, the data transfer was bursty in roughly minute intervals, alternating between moments of 50% net utilization and 15% utilization.
Subsequently, watching the throughput during backup, the net card saw a more more consistent 25% utilization, and about 28 MB/sec to the disk.
As for new observations on the WHS software, I've noticed the Start menu contents are substantially trimmed down, relative to a regular Windows 2003 install. I had a need for one of the items (Control Panel) and it was easy to reenable it in the Start menu Properties page.