Had the same problem with a IBM Thinkpad (600E) model.
Basically, wouldn't hold its charge, even though it was charged up every night and would go from near 100% full to 0% (shutdown/standby etc) within a few minutes once off the charger.

IBM replaced the batteries about 3 times under warranty.

Turns out that my Business Partner (whose laptop it was) was running down the battery each time he used it before recharging (which is what you used to have to do with NiCad batteries), but this is totally the wrong thing to do with your Li-ion batteries (which I told him many times BTW not to do this) - with Li-ion batteries you never run them down fully, and you charge them up fully at the first possible chance.

Doing that I've never had a battery go dead like that on me, but I suspect my current Thinkpad battery is starting this behaviour now after 1.5 years of use.
(goes from 100% on standby to a few % over a weekend on standby with no usage - sounds likle a dying battery to me).