I'm personally holding onto my Core2Duo until a general-purpose processor with 32 cores is available to consumers. It's completely arbitrary, but 32 cores is for me, psychologically, the point where it feels like a crime not to design a program in a concurrent fashion.

Picking such a buy-threshold also has the added benefit of suppressing any desire that I might have to update to the latest and greatest. I look at something and I think: "Well, that's nice, but it's no 32 core processor."