After getting the flu about 5 years ago, I usually get one each year, and haven't had the flu since. I didn't get around to getting the shot last year, and it was too late by the time I remembered (I had been on vacation the week my Dr. had the flu shots).
For those who say they get sick after the flu shot: most shots contain killed flu virus, which should not/cannot make you sick. You may have been exposed to the flu, and were infected just before you got your flu shot. Also, any doctor would tell you that no vaccination can guarantee you won't get the illness. You also can have the flu without having symptoms, although this is unusual. As one usually gets a flu shot during flu season, it would make sense that one was probably already exposed to the flu, and therefore, may have been infected just before getting the shot. It is possible, however, to have an adverse reaction to a vaccination, which varies in severity among individuals.
Ok, here's some proof I just dug up, which says what I always thought, in case you don't believe Dr. Marge:-):
http://www.cdc.gov/FLU/about/qa/flushot.htm#cantheflu