When stopped, rebound of the original anxiety is common as well as new anxiety. Slow tapers over the course of weeks to months usually keeps withdrawal and rebound to a minimum. A small subset of people are very sensitive to this withdrawal even with slow tapers. If you take benzodiazepines steadily for beyond a month, it is certain that you will develop some degree of physical dependence. Benzodiazepines have a very small potential for abuse, except in people with histories of substance problems.
Tolerance does develop to the sedating properties of benzodiazepines virtually all the time.
Tolerance DOES NOT develop to the antianxiety effects. Tolerance to the cognitive and motor effects is inconsistent and usually only partial. Because the actual sedation wears off, it usually does not make sense to use benzodiazepines on a continuous basis for sleep unless the benzodiazepine is being used to fight anxiety or mood lability which interferes with sleep. On the other hand, there are people who have very successfully used the same dose of a benzodiazepine for anxiety for 10 years or more. Antidepressants do sometimes cause physiological dependence with a withdrawal syndrome if they are stopped abruptly, but have no potential for abuse and do not cause DSM-IV abuse or dependence.