Like Peak Oil, a true post-antibiotic era is a milestone that I fear many of us will experience within our lifetimes. So many medical and even dental procedures will no longer be "routine." Gangrene, septicemia, and even TB may become commonly used words again.
A part of me feels dread about that eventuality, but then again, maybe this is simply helping to restore some balance to things and is not the apocalyptic situation that it sounds like, at least not for us in the industrialized world. Historically, the bulk of the reduction in deaths from infectious disease were due to wider availability of food, clean water, and sanitation. Antibiotics and vaccines, at least in the West, primarily just mopped up what little was left.
So even without any effective antibiotics left, humanity would reset to a new equilibrium with bacteria. Yes, many more people than we are accustomed to now will likely die from infections and we will again suffer through more diseases, but people will carry on and humanity overall will not face extinction like in some Hollywood pandemic movie.