"I've recently built up two midrange Core i7 based systems, which I discuss on my blog at Improbable Insights. One is based on Bloomfield, more specifically, the popular (among performance enthusiasts, anyway) Core i7 920. The other is the new Lynnfield-based Core i7 860. What's interesting is the similarity in pricing between the two systems. I'll talk about the individual system builds, but I also want to explore why you might build one type of system over the other.
These systems are similar, but don't have identical components (motherboards obviously differ.) But they are good case studies into what to think about when building a system that has some legs.