eDRAM amount/speed not yet known.
Thanks to Alstrong on B3D and PCPer who did the teardown:
TL:DR: Wii U has 2GB of Samsung DDR3 memory running at a max speed of [12.8 GB/s].
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.
17 was a guess based on the maximum speed of the Samsung RAM (1066Mhz vs. 800Mhz). Anandtech unit had slower Hynix RAM.
Comparison to other systems by Durante:
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
GTX 680: 192.2 GB/s :P