I think the idea of sheldon and penny in any sort of relationship would ruin the whole concept of the show, but perhaps an arkward encounter, involving the sexual nature? or penny tries to teach him how to kiss, or something along the lines of that.. I hope nothing big does go on between the two, because it would ruin the amazing idea of sheldon himself.
Since amy has joined the show, am i right to think that the viewer ratings has gone up? The writers would of not put amy in the show if they didnt think she would become a good, reconised charecter. I think she brings out the side in sheldon that hasnt been seen before, and as we all know, the show would be nowhere without dr sheldon cooper!