It's not virtually impossible. It may be virtually impossible in crappy cheap boards from Taiwan, but if you're buying cheap parts then you're likely not making money off the results that you're producing.
At the moment, the second fastest Xeon E3 (of those with integrated graphics) is $15 cheaper than the equivalent i7. They're not price-competitive with the i5s (which lack HyperThreading), but the E3 processors have been very competitive with the i7s since their introduction. The only downside is they don't get put on sale the way the overclockable consumer parts do, and they aren't widely known.
