Not to beat the dead horse again but scientists have finally put some constraints on black holes that would potentially be created by colliding particles*, and they've made a nifty prediction as well. Simulations done at Princeton suggest that to create black holes at the LHC (or any particle collider), the total energy of a single collision would have to reach one-third of the Planck energy.
Planck energy is (naturally) related to Planck length. If the Planck length is thought to be the smallest measurable unit of length (a very, very small 10-35 meters), Planck energy is the most energy that one can fit inside a 1 Planck length cube. Since we're talking accelerators here, Planck energy is about 1019 GeV and the LHC is only supposed to reach 14 TeV (roughly 103 GeV), so there's a long way to go before accelerators reach one-third of this number.
That said, we've heard lots about the potential of very small, curled up dimensions in addition to the three we're used to operating in, especially when it comes to string theory. This would seriously effect the limits for the creation of black holes if true and could bring the energy scales required to a much lower level. Even though the scientists don't expect to see black holes created at the LHC, seeing them would lend credence to the idea of unseen dimensions and, perhaps, string theory itself.
*No worlds will be destroyed by the creation of black holes at particle colliders, if at all possible.