i do calibration once a week or sometimes once 2weeks depend on my usage.
my macbook black is 9months old and 23 cycles, battery life still in good condition.
also, dont take out the battery when u using it and on power cause it will reduce the performances.
sometimes my macbook show i got 8hrs if usage when i turn on but when u start using it...it gets to 4-5hrs.....
so pls do calibration once a while to let the battery "juice" flow...

same situation here..i think the new 10.5.6 update cause it...not sure