I am also quite pleased with the battery life. Last week I got more than 50% battery left after listening to music for 9 hours over a BT headset. My previous Nexus S was dead by that time.
Today, I ran the battery down and then recorded data points while the recharging phone was turned off. A 1200mA charger from my old N86 was used. The result is appended below. As can be seen, the charging is not a smooth function of time. It charges up to 50% within only one hour, the next 40% take another hour. The final 10% then take 1 hour and 10 minutes for a total recharging time of 3 hours and 10 minutes. Beyond 90%, the curve has a kink. So it is not gradually charging slower as it approaches 100%, but also slows down considerably for the last 10%.
cheers