No, not doing WHS - considered it early on. Most of my problems came down to BIOS settings, RAID limitations, and the fact that my array is huge.
I broke down and loaded Vista Home Basic. Along the way I discovered an incompatible BIOS setting that probably would've let me install XP if I really wanted to, but I still had the problem that there's no way I could get all my drives under 2TB because the Intel onboard RAID only lets you have 2 drive arrays, and when you make the second, it automatically uses whatever is left - so if the first one was 2TB, the second one would be 2.2TB, and XP had issue with that.
So I went with Vista Home Basic - stripped down without that fancy aero effects or anything. I carved out enough of a system partition that my remaining data partition would be no larger than 4TB, as that seems to be the point where Vista choked, or at least it seemed so on early testing. Also when I first got into Vista, it wasn't letting me create logical drives over 2TB - but at least it was seeing the available space... I couldn't find any way in the GUI to convert to GPT partitions, but I did find you could do it from the command line using DISKPART - select disk 1 - convert GPT. Then it let me make a giant 4TB partition.
Got it all loaded over the weekend and got the HDHomeRun up and running and threw a bunch of shows in the favorites so we can start getting some things stockpiled - then I'll hook the HD Extender up to the TV and see how the wife likes it. It's running on the end table right now in the LR - needs to graduate to the big-screen TV.
I will say mapping Comcast's QAM channels is a PITA - and I still missed one of our favorites, so I'll have to tweak on that later. Next decision is whether to grab another DTV box for $5/month and try using that, or bumping up my comcast to include an HD Box - $50/month more now, but could save me $20/month if all works out and I ditch DTV.
For anyone still reading, I do have a question for the masses - how many people use an HTPC vs. an extender for the livingroom? I respect Dan's advice to skip that and go with an extender, but there's still a nagging part of me that would love to have a single device/interface for everything SAGE related, the ability to get to XM (through Tiversity or something like that), blue-ray, netflix streaming, hulu, itunes video, ElkRMS perhaps, etc - all from one place. I'd continue to keep the Sage server separate, but still struggling a little with that one. I'm also definitely worried about control issues. I do already have a PC hooked up to the TV, but it's just a basic business-class desktop - but I could add remote control to it and whatever software I want - right now we hardly do anything with it. Is something that simple a total pipe-dream?
Edit: I will add that my wife is pretty technical... hell, she has a computer sciences degree - I don't! So while she's lost most of it now that she's out of the field, she can handle the basics pretty well - but we won't want windows messages getting in the way, or to have to grab the keyboard at some point while trying to watch a show to fix something - that would irritate us. We want the basic functionality - being Tivo/Sage, to be almost appliance-like.