The battery hasn't been registering 100% charge, and hasn't been lasting nearly as long, but for the last few weeks I've noticed that if I run it all the way down, instead of the laptop going to sleep gracefully as it's supposed to, storing the contents of memory to disk before the charge is entirely gone, it just suddenly shuts off, losing whatever I'm doing. The other night, the battery display gained a little warning symbol, and the status said "Service Battery." Well, OK then!
I hopped over to Apple's repair web site, entered my serial number and a little about the problem, and clicked the link to have them call me. I was on the phone with a support rep in under a minute, he confirmed that my MacBook Pro is one of the unibody models, which means he can't simply ship me a new battery (oh well), and he passed me along to the dispatch folks. They're shipping me a box, I'll put the laptop in and send it off for repair, and in a few days, they'll send it back with a new battery installed.
Instead of the box approach, I could drive my laptop to an Apple Store, but they would then just have to ship it out themselves. It would cost me a few hours and wouldn't gain anything, so I'll stick to the box.