I frequently see complications of overuse of antibiotics. C diff colitis (1) is certainly the most obvious, but resistant pneumonias and urinary tract infections are becoming more common as well.
Many resistant organisms set up shop in chronically ill patients who see multiple rounds of antibiotics through their lives; however, in just my short 10 year history as a physician, the increasing amount of resistant staphylococcus (specifically MRSA) and VRE (2) found out in the community has changed how we treat many suspected infections.
Although some of this is due to overprescription by the healthcare profession, there are likely other selection components in our environment. Just as you can buy these antibiotics for animal use, so can people raising livestock. The FDA realizes this is a problem. (3)
Personally, the sad part to me is that our medical system is so expensive that treating routine, mild infections can cost hundreds of dollars. Thus, people search out these alternative riskier, but cheaper methods.
(1)http://en.wikipedia.org/wiki/Clostridium_difficile
(2)http://switchboard.nrdc.org/blogs/slyutse/resistance%20graph...
(3)http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm378100.ht...