Hi! In Apple.com there an article about this subject. They say that the secret to make your battery life last longer is to keep electrons in movement. So it's important to keep charging and recharging constantly without reaches 0% or 100% fo charge. You can make this plugging and unplugging the power chord 'round 20% or 90%. This can be borring but I think worth if works.
But in Apples, site there are another advice: just keep the power chord connected. When the battery is fully charged, the led indicator will turn to green, wich indicates the power will not pass through battery anymore. With my old Powerbook I always make this nd lost the battery very quickly.
One thing more: in System Profiler there are a cycle counter, thats indicates the number of battery cycles of charge/discharge. If you reach 3% or 97%, it counts another cycle. Apple says the battery have 300 cycles before start lost capacity. Does anybody have something to help with these questions?