Smoking rates do seem to be down, as a result of sin taxes and smoking bans in public areas like restaurants. However, although this might be an example of when Bentham's moral science might seem to work (although it is controversial how helpful mandatory sentences may be) it is hard not to think of a familiar phrase: "one man's meat is another man's poison" -- in short, what gives pleasure to some might not give pleasure to all. A good example of this might be a child who is starving for parental attention. The child begins to 'act out' and is punished. The parents think they are acting to deter the behavior, but in reality, rather than experiencing an intense and swift punishment, the child experiences the punishment as a kind of reward, because it is at least feels like some kind of attention. Another example might be that of an individual who enjoys flouting the law or ethics. Some people might like to take advantage of a corporate expense account, not so much for the pleasure given by the stole items, but the pleasure of getting away with a petty crime, which should not rationally exceed the possible painful consequences of getting caught.

Although it might seem as if incarceration is always a terrible punishment, it could be noted that the 'calculus,' that the punishment must seem worse than the possible pleasure accrued from the action, will not be...

A wealthy individual might think twice about committing a crime because of all he has to lose in terms of financial and social stability. A poor individual who believes he has no way out of his circumstances other than to commit a crime will likely see his situation far differently, and not view the threat of prison with as much fear. Also it could be added that in some instances, like a person addicted to drugs, their moral calculus may not function 'normally' as the punishment-setter. The wealthy individual might be addicted to heroin and feel that it was worth risking everything to get the drug for their 'fix' although logically most rational people would believe that no drug would be worth the loss of one's liberty, position, wealth, and power.
There may also be a certain injustice in Bentham's calculus because it refuses to take into consideration the individual circumstances of the perpetrator, which might demand some mitigating factors. Even if the punishment is not worse than the potential pleasure derived from the crime, punishment may need to have a rehabilitative component, as well as a deterrent component. Bentham's scientific moralistic calculus lacks individualized analysis, and since he is dealing with human moral actors rather than machines his system must fundamentally be found lacking in both humanity and effectiveness.