Many laptop batteries are Li-Ion, which doesn't have a memory problem. Some recommend that when you first get the battery, you should complete drain it, completely charge it, drain it again, then charge it up. After this, you should never let Li-Ion batteries drain completely. Again, no memory with this type of battery, so don't worry about partial charges or discharges.
90% of the time, I'm plugged into AC power when I"m on my laptop. Occassionally, I'll use the battery power, but only rarely since I'm almost always near an AC power source. My apt had power interruption issues last summer (seemed to go out a few times a week for a minute or less). Given this, I've always just left my battery in... If the power does interrupt briefly, if I don't have a battery in, say goodbye to whatever I'm working on.
I also run a utility called XPSpeedSwitch on my Dell I6000... This little utility allows me to force the processor to downspeed (to 700mhz I think) to enhance battery life, to stay at max speed (2.17ghz), or use Intel's default dynamic clocking. Many Intel laptop processors have this -- when the processor isn't being used much, it'll automatically downclock, though it'll go back up to rated speed when the horsepower is needed. See
http://www.diefer.de/speedswitchxp/ ... I also use that guy's I8KFanGui utility, which gives me direct control over fan speed.