They are more common on higher resolution screens. Sometimes they clear if you massage the pixel with your finger or flash a quickly changing pattern over it. There are websites with pixel-clearing animations.
Apple may or may not replace the laptop as they apparently allow up to 3 on laptops:http://www.engadget.com/2010/11/05/a...alies-accepta/
I'd give it a few days to see if it clears and if not, try to take it back for replacement and make sure to back up your data as they won't migrate it.