Bad example of evolution. The problem is that all that really happened were that those bacteria of a given species which had a natural immunity survived and grew in numbers. They didn't change in any real respect any more than a group of homo sapiens living near the equator became anything other than dark-skinned homo sapiens (has it never intrigued you that, despite the outward diversity of all the human "races" there are no new types, all are one species). It is a well-known fact that take away the stressors (i.e. the antibiotics) from a given bacterial community antibiotic resistant strains will reduce in numbers to pre-antibiotic characteristics within a few generations (much the same happened to the famed peppered moths of industrial England when the factors became less polluting). The phenotype was present all along in the bacterial communities and never completely disappeared, they simply reassert when conditions change. And that result is replicable, making it scientific fact.
Well, I'm far from an expert so I may be wrong in the details here, but:
As far as I know, this is exactly what we should expect to see according to evolution theory. With bacteria it all happens very quickly because of their fast metabolism.
How can a bacteria be resistant to drugs created by humans fairly recently? How can bacteria ingest substances that humans started to manufacture within the last seventy years or so (nylon)? As far as I have understood it, it's because of random mutations (that happen all the time). Most mutations would go "unnoticed", while some would - if the environment changed accordingly - become an advantage. Add the pressure of an antibiotic, and the bacteria that have no resistance will obviously die, but the few who survive will do so because they have mutated and evolved the capability of surviving the antibiotic. Not because they 'knew' what had to be done, but for the share 'luck' that those few bacteria happened to get the "right" mutation at the time in order to be resistant. When there is no antibiotic present, some bacteria would probably still mutate to be resistant to it, but it would not prove to be an advantage over the other bacteria in that antibiotic-free environment.
When the environment returns to 'normal', the specialized bacteria that were resistant fade away, because they were adapted to the particular environment where there was a pressure from the antibiotic, while recessive genes will have (perhaps) "left behind" a group of bacteria that suits the 'normal' environment.
Same with moths; the environment changes to favor darker moths (trees get dark for instance), and the darker moths get more offspring and get eaten less frequently than the lighter version. The environment changes back, and the 'light gene' again becomes predominant, because the infrequent light moths would again get more offspring and get eaten less frequently than the dark.
So - where does actual change (speciation) come in? That would be caused by a split of a species in two by the simple fact that they could - or would - no longer have offspring with each other (one group with the other). Separated, and let to breed in different environments over a long enough time period, they would gradually change (or rather, a new generation of each group would be more adapted to their current, separate environment than the previous generation). "Environment" here can mean everything from predators, disease, ability to find food and attract the opposite sex, weather, etc.
Of course - change within one species would happen for the same reasons as above.
Humans as we know them have only been around for a 100.000 years or so, which is little on a geological, evolutionary time scale. Plus, I personally think that the fact that we have self-awareness and the amount of intelligence we have, "disrupts" how evolution usually works in animals. Humans can make decisions that for an animal would seem very strange; 'breed' with someone who perhaps does not look as 'fit' (for breeding) as some other person, is not as wealthy as some other person, etc., or move to a place that is known for bad weather, but choose to move there anyway with hopes of surviving not by being adapted, but by modern equipment and one's own ingenuity.
So it's hard to say how humans will change over time.
