4 RMAs for the same card? Damn, some of you are far more patient than I am. After the second one I would probably just cut my losses. I do agree though, having a lifetime warranty is not much good if you have to use it over and over again.
And what is it about video cards that have such a high failure rate? I've definitely seen more video hardware fail that just about anything else, except maybe hard drives when you get a defective batch. Some local vendors offer "product protection" which is basically failure insurance, $30 might get you 3 years no questions asked replacement, might be worth it to some.