So, last night I took my black C2D in, this is the second MacBook I've had. Note that I didn't have any issues with my first revision and this is the only thing I've had wrong with my C2D over the CD.
Anyway... The laptop has been flaky at best lately, but I figured out after the fact only while on battery power. I'd get random application lockups, the screen seemed slightly more dim than usual and sleep / wakeup had all kinds of issues. So yesterday I brought my laptop in to work as usual, plugged it in and fired it up. I log in and see a nice X stating I don't have a battery. I was kind of irritated because this happened before and all I had to do was remove the battery while connected to power and reinsert. This time that didn't work. So I set off to reset PMU and PRAM. Hmmm, nothing, still no battery. The status lights on the battery showed there wasn't enough juice to run the laptop (last dot flashes rapidly when you press the button). I was annoyed because I frequently take the MacBook around the office. Grrr.
So I'm off to see the Genius Bar. Now, let me just state that if you go to the Genius Bar and you want your white MacBook case entirely replaced don't expect these guys to do it that night, a half hour later because you are supposed to go on a trip tomorrow and were too lazy to come in any earlier. I'm sure the symptoms did not show up overnight.

Anyway, back to my battery. I waited patiently and finally it was my turn. I was fully prepared to argue the battery replacement because I didn't want to part with the laptop for any amount of time. But, the guy just did the paperwork, didn't even turn the laptop on or check it out (other than for the serial #) and said he had one in stock and would go get it for me. Now, the ironic thing is the lady next in line had a C2D with the exact same problem. That Genius told her that they've seen a lot of that lately and they are aware of the problem. Surprisingly I haven't seen much fanfare around this from Apple geeks. Did I miss something?
If not, and your MacBook (maybe the Pros too, I have no idea) is acting flaky on battery power -- be forewarned that you're probably going to be taking a trip to Apple relatively soon.
The best way I think people will find out if there battery is toast is to completely drain it. I mean, let it warn you and put itself to sleep. Then try charging. I had looked at the # of charge cycles that were on the battery a few days before I took it in and there were 48. iStat Pro said my battery "health" was 100% -- and I can't say I've ever seen that at anything else.
But anyway... FYI!

And props to the Southdale, MN Genius Bar. They're always pretty decent. Especially compared to the few bad experiences I've had at MoA!