Someone mentioned before on this thread that it's common for Electrolytic and Tantalum capacitors to have opposite polarity markings, are we *absolutely positive* that doesn't explain the confusion here?
I *seriously* doubt these machines shipped with an electrolytic capacitor that was put in backwards. Electrolytics have this nasty habit of blowing up like bombs when run in reverse (seen it in the flesh several times), and even if by some miracle that didn't happen it'd still heat up and act like a (partially) shorted circuit. This is the sort of thing the manufacturer would have noticed after shipping a few thousand units.

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I thought the same way at first -- we have to be thinking something wrong -- but look at the multimeter picture closely. There's -5V across that capacitor. And bbraun confirmed the same capacitor orientation on his LC III.

It's backwards. Unless Apple had a special batch of electrolytics made that had the black mark on the positive side...and used it only on that capacitor...

I don't understand why it hasn't popped either. My understanding is that electrolytic capacitors in reverse can explode nastily. Is there any explanation? Not enough current available from the -5V rail to do any harm? Maybe the original capacitor, even though it has a polarization mark on it, happens to be bipolar? I'm just trying to think of any rational explanation other than "it's backwards" and I'm coming up blank.