Return of the Living Dead... Pixels...
Apple makes it clear in the documentation that came with your Powerbook that a
certain number of dead pixels is considered acceptable, and there are literally millions of the little suckers. The rubbing thing can work, but I'd say be very careful, the "gently" thing is the key, and voiding your warranty is not a good idea. Check with Apple if you just bought it for a clear ruling and the go ahead on the rub down.
If I remember correctly, I've seen posts here that say that up to 6 or 9 is ok. The big thing to consider of course is that if apple replaced all the one-dead pixel screens that came off the assembly line, Powerbooks would be at least 15 thousand dollars a piece.
Apple's Powerbook LCD displays use addressable pixels. The pixels are composed of subpixels (one Red, one Green and one Blue for RGB).
Any one of the transistors that turn on each of the red, green and blue pixels can be faulty, resulting in an off color. You mentioned you have a black pixel. I'd be sure to verify that by putting the pixel(s) over various colored backgrounds, red, green, blue etc.
Each subpixel has a corresponding transistor responsible for turning the subpixel on/off.
If one of the transistors to the red, green and blue pixels does not function it can represent as dark (a black pixel as you mentioned).
Detailed information can be found at Apple on what to do from
Apple Technical Document 22194.
And remember, this isn't just an Apple display thing, it's everywhere. Powerbooks are actually much better where this kind of thing is concerned compared to non-Apple displays.
