I think I have the newer iWatch, so I'm unsure about previous models, but I can get a full two days of use out of it. It's actually a bit of a downside for me since I always forget to recharge it :-)
ugh, the timer! Do you use the chronograph watch face too? I always accidentally hit the stopwatch and 3 hours later realize it's been running the whole time.
Some days it barely gets a day - still haven't figured out if this is due to excessive timer usage (kids!) or messages or something... but it's rare.
I've slept with it on and simply put it in the charger while I shower/dress/eat and it's full.