There is a theory from some guy around the web who says only Samsung drives shut down properly on the BP6. I posted a link to it here on the board, will search for it later. Personally I had trouble with three different Seagate drives on the HPT366, no probs with a WD 20GB, Fujitsu 40GB, Samsung 120GB.
But it might be the power connector or PSU. I recently encountered occasional freezes on my BP6, and the DVD burner (on the standard IDE) first refused to burn DVDs, later I couldn't even burn CDs.
The culprit were the power connectors. Or the PSU itself, I'm not absolutely sure. I replaced it and everything is fine, the DVD burner works perfectly, no freezes at all.
BP6, RU BIOS, XP SP3, ACPI, 2x366@523(1,95V), Pentalpha HS + 1x 12cm fan @5V, 768MB, Powercolor Geforce 3, RTL8139D NIC, Terratec EWS64L, Samsung M40 80GB (2,5''), LiteOn CDRW