Me. I'm using it. But don't try it unless you really have more than 3 GB of RAM: the driver support is really bad. Anyway, my photo processing rig is:
C2D e6600 @ 3.6GHz (50% OC), 320GB SATAII HDD, GeForce 7300LE, Asus P5K (P35) board, 2GB Kingston PC800 RAM.
The whole setup was put together for about $1200, minus monitor. Despite having only 2GB of ram, Photoshop CS2 + Lightroom fly even when run simultaneously (and working with RAWs). SpitFir3 definitely got that right.
EDIT:
My advise: Your processor's L2 Cache should be greater than or equal to 4MB. Don't be tempted to get the E4XXX series Core 2 Duos. They're not worth it. (and neither are Netburst architecture processors)
Yes. CPU efficiency is the most important thing. Currently, clock for clock, C2D is the best.
When doing batch coversion of RAW, the CPU is hit the hardest. Open up the task manager, you will see 100% on single core or 50% each of the Dual core.
Is the cache really important? Running a E6300@3GHz. CS3 is fast, tot of getting a E6600 so that I can clock higher. Currently limited to 400Mhz FSB by motherboard.