Most (but not all) companies use a standard return policy for the LCD (there is an industry standard, I have it at home in a pdf-file, but do not remember the name). If I remember it correctly it allows 1 defect pixel (black or white), if you have 2 you can return the TFT. And it allows 2 defect sub-pixels (green, red, blue), if you have 3 you can return it. I know at least some manufactorers, that use this standard. However it is not legally binding, some companies may not follow it, but I have also heard, that some companies are now offering, that you can return their TFTs with just one dead pixel, so they go beyond this standard.
Bottom line is, that you should check the return-policy, before buying a TFT (most vendors have that either on their website or will react to an email).
I have one dead pixel on my LCD (white). I only see it, if the desktop color is quite dark, but not in any games or office applications. It is no problem for me, except, that it will lower the price of the LCD, if I would try to sell it. When I contacted Eizo and asked, if I can return it, they sent me the file, I mentioned above and told me, that I can only return it, if it had 2 or more dead pixels.
Cheers
Speedy
P.S.: For no money in the world, I would go back to a CRT. I love the additional space on my desk, the crisp picture of the LCD in both office apps and games, the non-relevance of the 60hz-bug via DVI. But of course this is personal preference.