Wait! I think I know why people are getting confused!
The ratings Craigg listed are not Watt*Hr (or total energy), they are Amp*Hr! (Check around the web - this is shown at many stores).
The capacity is 6.6 Amp*Hr (6600 mAh as some say) for the 9-cell and 4.4 Amp*Hr for the 6-cell. But the Amp capacity is useless without knowing the potential of the current, which in the case of a ThinkPad battery is 10.8 Volts.
10.8 Volts * 4.4 Amps*Hr = 47.52 Watts*Hr. Since Watts = Joules/Second, a Watt*Hr is a measurement of total Joules or energy capacity of the 6-cell battery.
The new 6-cell batteries are 4800 mAh, or 4.8 Amp*Hr. Using Volts * Amp*Hr, we get a a design capacity of 51.84 Watt*Hr, which is in line with what Craigg observes on his T43.
My ThinkPad averages about 13 Watts with WiFi on and screen at half, and moderate usage. 51.84 Watt*Hr / 13 Watt = Approx 3.99 hours runtime.