After 300 loadcycles, the battery in an early unibody MacBook Pro is kaput. Period, says Apple.They will not replace it if its capacity has fallen, because it is at the end of its intended lifespan. Three hundred is not all that great when compared to the newer unibodys which are supposed to withstand 1000 loadcycles, but is decent.
Fortunately for me, my battery is still going pretty strong even after 400 loadcycles. As you can see from the image just below, coconutBattery shows that it is still above 90% of its original capacity. Note that the battery that was in the laptop when it came from the factory was defective, and Apple replaced it a month into my ownership. So that 19 months in the picture is actually only about 18 months.
UPDATE (July 16, 2011): After 750 loadcycles and 32 months, the same battery is holding 86% of its original capacity.
UPDATE (March 28, 2012): After 980 loadcycles and 40 months, the same battery was holding 85% of its original capacity. Unfortunately for me, I killed it by spilling water on my desk.
I replaced it with a "Techno Earth Battery" from Amazon.com. It has the same capacity as the original battery, but only cost half as much.