i'd agree with eq. I dont see much of a difference between using a high end quadro and nice gamer cards. However, rendering time certainly is improved with the quadro at work. but thats not so much gamedev related.
IMO quadros simply arent worth it, you get way more for your money just buying say a 8800 or something. Theres no real value in that market, they make cheaper quadros but those are even more worthless. As CB says, they're mostly good at things like, drawing antialiased wireframe and shit with tons of polys, totally useless…