The LHC smashes particles together, creating alot of energy. As this energy expands, there is nothing to fill the space in between, and so anti-matter is made. So yes, they WILL be making black holes, but the black holes will only be on earth for a millionth millionth of a second, and will be the size of other particles. Not exactly the earth-eating sized monstrosity everyone makes it out to be. The only thing that could go wrong is that the particles acccidently split instead, creating a nuke. This would be very bad for the health and safety of the scientists..... and switzerland for that matter. Not to mention that this is a $10 billion science fair experiment..... Remember, they are using Hydrogen, so it could be a hydrogen bomb. But that is very unlikely, as they are only using the protons from hydrogen.... Not an actual hydrogen molecule. I read somewhere that they described it something like this:
"Its like throwing billions of wind-up watches at each other, so that they smash into their many componants, and then observing the broken parts on the ground to try and understand how the watch works"
Another thing that MAY go wrong is that they 'lose' the mini black hole they created. If they make it, and it is unexpectidly stable, it may not just 'dissapear'..... and will be drawn in by earths gravity and sink to the core of the earth...... slowly eating away at the core. But remember, its the size of atoms.... so it wouldnt exactly be eating very much of the earth....