I'm in a bit of a special situation because I work in IT for an enormous global company. When something goes wrong and my "expertise" is needed, no one cares about vacation time anymore. We're expected to just get the job done.
It's also tough to find holes to take the 4 or 5 weeks of PTO that I get each year.
My boss also offers me "comp" days quite a bit. On those days, I work sparingly but I don't take an official PTO day.