I got a chance to play with a couple of A123 packs. My LHS let me borrow some to test. I was impressed with the performance and the charge time, but they are rather large. A 5S2P pack is about a large as I'm willing to go with the A123 while still maintaining some sort of balance.

I will try it one of these days, but for now, I can't justify the cost considering that I can get a 5S2P 8Ah pack from Truerc for around $140.