I've used Irish Moss in every ale I've ever brewed. While it's supposed to coagulate and settle out proteins at the end of the boil, I still experience a good amount of chill haze. I recently read that whirlfloc tablets are concentrated versions of the active ingredient in irish moss. If you are concerned with clarity, the same source recommends using whirlfloc at the end of the boil along with SuperKleer K.C. and Polyclar in the secondary. Personally, I think it's a matter of brewing technique--i.e. utilizing a full-wort boil if you have the capabilities and having control over your steeping. Check out this month's BYO about steeping specialty grains. If you combine careful steeping with a full wort boil, you'll reduce haze and off-flavors considerably.