An atom smasher is to a black hole as a match is to the sun. Not too much to worry about.
Unlike an active star, there doesn't appear to be any limit to how small a black hole may be. Well there sort of is, but it is due to quantum mechanical effects, and would be quite small indeed. In fact that's part of the argument for this thing not being dangerous. The smaller a black hole is, the faster it "evaporates", due to higher tidal forces near it's event horizon, according to Hawking at least. Since the LHC could only create very small black holes, they would be expected to evaporate faster than they could eat. I hope he is right, and expect that he is.