It all depends on where the pixel is and what color it is. My laptop had a dead pixel that was colored light blue. It also happened to be 1/4 inch off center, so it was VERY noticable.
Interesting thing, though, in about a year, it managed to fix itself (well not completely on its own, I had been told, correctly, that if you lightly massage the area around the dead pixel, you may manage to get it to properly connect to the power circuitry. Spent a few weeks periodically massaging it and it finally stayed connected one time, been fine ever since.) But take what my experience with a grain of salt, as I knew my pixel was getting power (otherwise it would have been black), so this method may only work in that type of situation.
Also note, that most manufacturers have guidelines for returning a LCD as defective depending on number and location of dead pixels. Some will accept returns if a dead pixel is within 4 inches of center. Others require 2 or more dead pixels to be within 2 inches of each other. And they might have a limit of say 4 to 5 across the entire screen.
Find out what their policy is. If they have a good policy, then don't be afraid to buy the LCD.