The best Nvidia card I ever had was a 5700LE. It never failed me in 3 months then I 'upgraded' to a 6600gt which had more issues than all my other gfx cards and cpus put together. Great card, it just never really worked properly.
Then I had an 8800gt which lasted 8 months before I had to RMA it.
To be fair, I've also had two borked ATI's though I was very impressed at how quickly I was given replacements for them. I read somewhere that ~1% of gpu's break - I must be at least doubling that percentage all by myself.