I have one of Ping's new 48V 20AH packs, and I tell you that for "cheap" lithium, this guy is your doctor to go to for an uplift!

So far I've pulled 35 amps out of it while riding up hills and accelerating, with no problems at all. Very slight heating of the cells, and a bit more heat coming from the cutoff FETs on the BMS, and very little
voltage sag: 0.13 Volts per Amp of current drain. This puts Ping's Ver2 packs them slightly ahead of Headway's offerings, who are not seeming to live up to thier specs so far.
I have yet to drain them over 10Ah yet, so only half capacity used so far. Even after this, the voltage was still around 52V unloaded! The minimum voltage point logged during this trip was
47.9V while drawing about 35.5 Amps, or about 1700 Watts. So far I'm very satisfied! I've boosted a small scooter I have been given, and it seems I will be able to go about 40km if the battery lives up to it's claimed capacity (yet to see).
I've charged the battery at 6 amps using a vicor DC converter and the pack stays cool to the touch - but the BMS doesn't! It's only the protection FETs at the end of the BMS heating up, but not badly since I can touch them without discomfort. Works great! I'll post some discharging and charging curves I've logged on the ping v2 thread later.