yes, i have.....
on one hand, it's been really helpful when i'm extremely congested and it makes me cough, it breaks up the mucus in my throat and i can spit it out (gross, but sometimes necessary). and like other people said, it "takes the edge off".
but at the same time, i've known it to prolong my illness. granted, some of those times were probably because i was smoking blunts, but i do remember specifically one time i had a bad cold which I could NOT get rid of. it persisted for a few weeks. finally, i gave up smoking for a few days (it was really hard but i managed) and within those few days my cold cleared up. you can make of that what you will, but i'm pretty sure that it was the smoking that was prolonging my cold.
when i say that, it was NOT the weed itself. i don't smoke cigs or anything, just weed....and it wasn't the actual weed, it was the smoke irritating my sinuses. but like i said in the first place, if you've got a lot of phlegm in your throat, weed can help you cough more to break that up and get rid of it. just don't go overboard. and don't share with others, unless they know you're sick and don't care!