Max Amps do a saddle LiPo pack - have seen it on their web site.
LiPo is an interesting one. I have tried it, and didn't notice any difference in performance to my IB SHV's.
I think that all Mark says is correct at the minute. However, i genuinely believe that if they got used widespread for racing - you would see things change. Who remembers that we were told NiMh cells didn't need discharging
I think if the major players got into the competition aspect, the pace of developement would be massive, no one would be able to keep up. Look at any new technology/application and it always goes this way - think Brushless motors/speedos now. Much greater rate of change when compared to conventional brushed.
Not convinced this would be good for the racers.