I use a Nikon DX Format camera (D300) and a FX lens (24-70mmf2.8), so using a UV as protection together with a polarizer do not result in vignetting. I do not remove the UV so as to avoid dust on lens front element and this also saves me time. Otherwise I will be fumbling with the filters everytime I change them. Some may say using two filters together will deteriorate quality. Maybe so, but I find it better than having dust particles all over the lens element and I have actually dropped a filter while fumbing. Also faster in gettuiing ready to press the shutter.
But I will have to fumble again when I switch to full frameFX. ;-)