Assuming you are talking about sore muscles here, and not joint pains etc....

I LOVE when my leg muscles are sore- because it indicates to me that I have pushed them again a bit further than they were built up to deal with. Sore muscles to me mean that when I go to sleep that night, my legs will be building MORE new muscle to compensate for what I am asking them to do.
Maybe I'm nuts, but to me sore leg muscles mean bigger muscles are going to be built over the next couple of days. I see it as a good sign that I am pushing my limit upwards and not just staying on a plateau.