As soon as the new Blackgold 6 in 1 tuners become more readily available, I will probably go to Freesat on the Media Center (each tuner card has 2 freesat, 2 freeview and 2 useless analogue tuners, all independent). A couple of those cards will give the MCE 4 freesat and 4 freeview tuners, which is more than enough for my needs. This can be streamed to the xboxes elsewhere in the house.
I agree, I've always liked Black Gold stuff so will be waiting for this as well. I'm using a single tuner BG Freeview card in this Scaleo E mce I built after seeing your thread on the other forum. It works very well on W7. 
I'm currently purely freeview, running hvr2200 dual tuner (excellent PCIe card (got '4' tuners, but only 2 can be used at any one time, and who cares about analogue!)) and a Nova DT500 dual tuner (not a great card).
Intel DG45ID mobo, Q8200 cpu, works well, though need to use audio driver from around October 2009, as the later ones cause a black screen requiring a reboot. All in an Elonex Artisan case 
I've kept both cases running the original mobo although I feel the inclination to follow your lead and upgrade the box I'm currently using to OOF and watch some telly through. (via a Radeon HD 4300 and HDMI lead)
This works quite well and I was surprised that the drivers for the BG were OK in W7 as the Dell I had the card in before this, which was running Vista, didn't like them at all.
I had so much trouble with the Dell I beat the keek out of it which is why I bought the two Artisan/Scaleo cases in the first place.

Anyway I rebuilt the Dell and it's running fine in everything but MCE mode.
One of the things that did concern me before starting the upgrade however was the case PSU as it doesn't appear to be readibly upgradable? but I guess that it's sufficiently powerful to run the additions - unless you were able to locate a different PSU.
I think the MCE is well worth the effort and an easy way to view and record the telly.