How Many Sets of Bath Towels?

Survey

We found out that most of you change your bedding for different seasons, but here's another setting-up-home question: How many sets of bath towels are ideal? We have two sets of Hotel Collection towels from Macy's and love them, and then one crummy set of guest towels.

Is the ideal number three, so that you extend the lifetime of your towels by not washing them as much? Or Is three a bit exorbitant? And should guests have a nice separate set of towels, or hand-me-downs?

Image: New Internationalist licensed for use under Creative Commons