Enthusiasm among extreme overclockers is fueling the C2 craze right now. The only real advantage I can see for C2 over C1 is the ability to more easily clock 500MHz+ FSB. For 99% of us, 500MHz+ is pointless since it won't happen out-of-the-box. For 100% of us, it's pointless since no one has shown a 500MHz overclock to be stable 24x7, which is important for anything more than running benchmarks (i.e. SuperPi and Prime95).
IMHO, the advantages of the P5B Deluxe over the P5B-E is more than worth the $40 premium. Heatpipe northbridge cooling. 8-pin EPS12V connector, which might provide tangibly better 4-core power support. Dual x16 PCIe (8x8 when CF or SLI). Black PCB. Dual ethernet (not an advantage to me, though). For an extra $20, WiFi.
And that's just right now, since the P5B Deluxe will be transitioned to C2 shortly.
But by all means, if someone intends to overclock for overclocking's sake, then the P5B-E is for them.