Chesty is a kneader. He does it during petting "sessions." He also sometimes does it when he wants to be petted--he'll jump up on the bed while I'm sleeping or just lazing around, then stand on my pillow and start kneading. He has never suckled, though he definitely drools when he gets really into it! He'll knead if he's lying on my stomach or lap, which is sometimes painful because he is a big boy, and his nails...usually I just take the pain, because I love the kneading. If it's getting bad, though, I'll put him on a pillow and continue petting.
I wouldn't discourage the behavior. It can be symptomatic of a cat who was removed from his/her mother too soon, but I also see it as an expression of love and comfort from cat to human. If it's getting to be painful, distracting, or otherwise uncomfortable, redirection seems to be the best strategy. On an earlier thread, one poster said that she dedicated a stuffed animal to be her cats kneading/suckling toy. It probably took a while to do so, but the cat continued to use the toy for years, as I remember.