Uh, unless you are going for SLI, there is no real need to go for the 680i. The P965 boards like the DS3 and DQ6 from Gigabyte do the same for cheaper. I'm not to up on the overclocking potential of the 680i, but from what I've heard, its around the same as the cheaper P965 boards.
Here is a different issue though. I think Penryn will use a different chipset am I wrong? Whereas Barcelona is suppose to work with AM2? I could be wrong but this is my understanding. Also when will they start cranking out DDR3? Penryn with DDR3? Unlikely but would make things interesting. Would be interesting to see if they plan on making the transition ever/someone within the next 2 years.
Like most have said above, there is nothing that we can trust right now to go on as far as K10 and Penryn are consered. AMD and Intel have released there own test of how powerful they are, but that really doesn't say much until the possessors are out there to test.
Unless you've got absolutely no need to build a rig and are just doing it because you've got nothing better to do, don't wait for K10. So far, AMD hasn't given anyone a reason to wait for K10 because they haven't shown proof that it can even compete with C2D, much less Penryn. That doesn't mean it won't, but so far they haven't shown anything worth waiting for.
So if you want to build now or very soon, just build C2D. I think the 680i and 965 will take Penryn but nothing's been officially stated so who knows. For 680i boards, the EVGA is very popular, I have one myself. The Striker is overpriced, but the Asus P5N32-E SLi is also good.
the best advice for those who don't want to wait continues to be to build AM2 now with a modest priced chip, and do a drop-in upgrade later, when needed.
If you build with a motherboard that will not accept a drop-in upgrade, you extra future costs will include a new motherboard, a new Window's licence (for OEM Windows), for a total likely well over $200. So knowing what the upgrade path is has wallet implications.