To fold with my 2.6 Celeron im using 89 KW/h which at my power rate is costing me $6.95 per month
My 2.2 P4m in my Dell laptop uses 45 KW/h costing me $3.47 per month
My Q6600 overclocked to 3.0 uses 134 KW/h costing $10.43 per month
And my PS3 uses 148 KW/h per month costing $11.59
According to FahMon my Q6600 gets 2730 PPD, the PS3 gets about 900 PPD (estimated), the P4m gets 130 PPD and the Celeron 78 PPD
So my Q6600 is getting me a little more than 8100 points per dollar
The PS3 gets me 2407 points per dollar
P4m = 1161 points per dollar
and finally, the Celeron only 347 points per dollar spent
So obviously the money (no pun intended) at least from my judging, is in SMP and the more cores the better