I never buy refurbished. Though, if it doesn't work, newegg will send another one, so if you're using newegg and you're buying say a very expensive part, and you can get a refurbished for a huge difference, go for it.
I am considering buying a refurbished video card from newegg. I buy their new stuff all the time with great results. Does anybody have any good or bad experiences with their refurbished products?