PCPer did a teardown. Great stuff... they actually read off the RAM chip (SMRT!). There's only 4 chips.
Samsung K4W4G1646B -> DDR3 4Gbit, 1.5V, 800/933/1066 speed bins -> I'm pretty sure that means "DDR3-1600/1866/2133" data rate.
256Mx16 would imply 16-bit I/O per DRAM... So... 17GB/s at most for main memory bandwidth. They didn't mention the rest of the numbers on the DRAM, but they ought to have high res photos later.
360: 22.4 GB/s, eDRAM for framebuffer
PS3: 25.6 GB/s main memory BW, 22.4 GB/s graphics memory BW, no eDRAM