I've built one C2D system this year (well, late last year) for family --decided to wait for one for myself (see what AMD's K8L/Barcelona bring to the table, as well as Intel's likely summer refresh). I used an Intel BadAxe mainboard for the build.
I can't say I fully trust nVidia any more. The SATA incident with their reference design 680i boards should have been caught before product release, just like the SATA incident with nForce4 and Maxtor SATA drives. While it has been fixed, I've seen a nagging trend in the past few years that concerns me when it comes to nVidia's level of support for consumers. There have been several broken products, some of them broken in silicon. Lately, driver support has been less than stellar. And to top it off, they are retiring support on some products quite early. This wouldn't hurt someone like Hox, who gets new product fairly rapidly, but for those of us who keep a mainboard for 2-3 years, this could be a concern, an example being the nForce3 chipset, which at first was not going to be supported under Windows Vista, and now is (due to customer backlash), only we don't know when.
At this point, the Intel BadAxe2 mainboard is about the only C2D mainboard I'd look at. It doesn't support SLI, but I never plan to use that. The i975X chipset is a little dated, but still has all the features, supports both new and legacy technology, and has really good RAID support. There are reasons why Intel chose to use it on their flagship (and only model with overclocking options) mainboard over the i965, though that chipset would probably be my second choice.
Intel Q9450 @3.2GHz, Gigabyte GA EP45-UD3P, 4 x 2GB G.Skill @4-4-4-12
Antec P160SW case (modded), Xigmatek 750w PSU
3x 500GB (RAID-5), , OptiArc 7200S, ASUS E818A3T
Creative X-Fi XtremeGamer, Hauppauge HVR-1800, Radeon 4890