Well, if you don't see it after reboot, then it's not a dead pixel, it's just calibration related issue, could be fixed by software update.
A dead pixel is something permanently on the screen. My first phone had one very bright dead pixel and 3 other sparkles, I took it back within 14 days and got a new one.
If you don't feel comfortable with it, you should take it back since it's not really a "cell phone" or anything with only 1xx by 2xx screen size. It's something you paid over $600 and you are gonna use it for a very long time.