mine's had maybe 900 cycles, and the battery literally would last 20 minutes after being charged all night. i got mine at the same time as you, december 06, macbook pro. its quite annoying, as it is no longer portable so to speak
I was planning on giving AppleCare a call tomorrow just to ask nevertheless but now feel my battery might be doing pretty well.
744 cycles and iStat Pro tells me the battery "health" is at 91%. The lowest i've seen the health is at 89% when when the Mac is running on battery and it's about to die.
I've tested my Macbook and the battery seems to last alone for about 2 hours on the brightest screen setting and only minor web browsing or heavy essay typing. Watching a DVD or Hulu or YouTube will knock it to about an hour. If I dim the brightness to a low setting, I've gotten an 18 page essay done within 3 and a half hours on just the battery, though i'd recommend writing an essay with a brighter screen.
When I hear you're saying it's only lasting 20 minutes it makes me feel better about mine, seeing as I need portability from my Macbook....
...The thing is, I can't for the life of me remember what the healthiest longest battery life I can get from my Macbook. I searched on eBay for batteries and it's interesting that there are original apple macbook batteries but also these off brand ones that still work but aren't great. The prices for the original apple batteries were like $70, while the off brand ones were $40-$60. The off brand models mentioned fully charged the battery will last about 2 hours. So not worth it since that's what i'm getting.
But i'm wondering what about the original apple batteries?
I wouldn't upgrade to just get an hour more, to 3 hours on a full bright charge...but something like 5 hours and i'm sold.