Socket 754/939 Performance
I fully understand that socket 754 matches 939 performance on the 90+% or so applications that aren't memory bandwidth limited. However, as our Intel partisans like to point out, it's not just the performance it's the perception. The perception is that AMD was castrating their 754s for marketing reasons. However, all this served to do is fragment the K8 infrastructure, as Joe eloquently pointed out.
Personally, I believe the K8 Semprons were a mistake for the same reasons.