It's still useful to control unwanted autocomplete behavior. With Chrome, for example, if you have a form with fields name "name" and "state", even if they have zero to do with a personal name or state of residency, users still get their normal autocomplete in "name". When you select a name, if that autocomplete entry has address information attached, Chrome helpfully fills in "state" with "CA". Even if "CA" makes zero sense for that field.

Almost all other times, though, I'm with you: slap them!