I don't enable GPS and network location. I'm on GSM all day, and occasionally 2.5G data transfer (no 3G with my SIM). I'm on wi-fi (100mW + max power saving mode) whenever I can. My battery doesn't drop a bar until the day after charging. I don't really have to charge more often that every second day, or, if I stretch it, the third day.

The battery did seem to get a little bit better after the first couple of recharges, but I don't have any real evidence to back this up.

I only keep an eye out for CPU-using problematic applications. Had trouble with pulseaudio once (caught it by the 'top' program), which caused the battery to discharge too fast, but other than that my N900 is behaving beautifully as far as battery use is concerned.

p.s. I repeat that I never use the GPS or network location.