The Kentsfields do run hot, but the reason that they run hot enough to destroy heatsinks and other cooling apparatus is that they're able to be overclocked a fair amount. A Q6600 at the stock 2.40 GHz shouldn't run any hotter than an X2 6000+, in fact, it probably will run a tad cooler if the same heatsink is put on the 6000+ and the Q6600. The Q6600 shouldn't be anything to avoid as long as it remains at stock speeds.
The QX6700, Xeon X5355, QX6800, and Xeon X5365 are extremely hot-running CPUs, especially the 2.93 QX6800 and 3.00 GHz Xeon X5365. I'd wait on buying a quad until 45 nm Yorkfield parts ship if I wanted one over 2.4 GHz. Either that or wait for the Agena, <obligatory AMD delay bash> but at least we've seen the Yorkfield benched </obligatory AMD delay bash> 😀