I still use Ni-Cd packs, mostly because they take a lot more abuse and don't require a regulator.

Although most of my batteries are still Ni-Cd, I have a very large Ni-NH pack and are seriously looking at using A123 for my next project. A lot of guys in my club that are heavy into electrics are very fast changing to the A123's and they are HAPPY!!!

I'm sure you'll be happy with them once you try them. I've got a Twist .40 with an 6.6v 1100ma pack and love it. I just finished a 4*60 and will probably put an 1100ma pack in it also although I have some 2300 cells looking for a home.

I charge my 2300 cells at 10 amps, thats all my charger will do. I do know of people who have built zip chargers who charge 2300 cells at 18 amps with hundreds of cycles and no adverse effects. Be aware that most older Li chargers aren't setup for the A123 cells since they require different charging parameters. IE, they are nominally 3.3v and not 3.7v like a normal lipo. Most of the newer chargers coming out have A123 capability.

For the Hellcat I'm building, I plan on putting 2 6.6v A123 2300ma packs in parallel on separate switches for the receiver and a single A123 2300ma pack for ignition. That should fly the plane for a while.