I have to agree, that "always on" (3G) sucks the battery dry within a few hours (I'd say 10 to 16 hours depending on usage of the phone) , but I usually can make it through the day.

I cannot agree with comparisons to other phones like the E71. I do have an E71 too and I really love it. Nevertheless, when "always on" (3G) the E71's battery is empty within twice the time, so let's say 25 to 40 hours with the battery having a slightly higher capacity.
Of course, this is definitely longer than the N900. However, it absolutely does not offer me all the possibilities the N900 does. That's starts with the screen and ends with the input capabilities. Compared to the iPhone: it may have a longer runtime, but again... in my opinion it's not as pleasant to use.

Still, battery runtime is an issue, but in my opinion, it's not that bad. As said, one big disadvantage the N900 has: it's so convenient to use you can't let your hands of it