I picked up one of these recently, to be able to work at a client's location. (Damn, Dell seem to have raised the price quite a bit since then!) Great performance, cpu/3d wise, and doesn't overheat; worst it does is make a slight noise when the fan starts. Lovely machine; if it could swivel the display to turn into a hybrid tablet, I'd want it to have my babies.
I haven't missed the numeric keyboard at all; don't worry about that.
Interestingly, even though I hook it up to a larger display at the office, I find myself using the laptop as the primary display anyway. I'd say one specification you definitely should pay attention to is resolution. If you get an 15" screen, don't accept anything less than 1920x1080.