I would say fucking up local water tables is a big one, the ability to set your tap water on fire, etc, etc.
I am all for sound science and have no doubt that fracking can be done safely and properly, but is this the case in the real world? If it were, there would be no accidents. Water is too precious to fuck with. There is a big movement against fracking here in Aus...whether the science says it is ok or not, public opinion plays a big part and in this case I am with majority opinion. I don't want to see our farmland put at risk (no matter how small that risk is portrayed to be).
Also, I just want to vent about coal mines while we are on the topic of fucking up water tables and farmland. FUCK COAL MINES, ESPECIALLY IN THE VICINITY OF PRIME AGRICULTURAL LAND.