Do you use them? I never have, I always figured another layer of glass without a specific purpose would do more harm than good as far as image quality was concerned. For purposes of lens protection I am thinking of changing my mind and investing in a new Hoya HMC UV filter for each lens. I'm sure there are as many opinions on the matter as there are members here, but I would like to hear some of those opinions and the reasons behind them. So, fire away!