I remember a letter in the Dear Prudence advice column about this issue. IIRC the letter writer had a particular way of using her bath towels - she used one side of a clean bath towel to dry herself off and the next day use the other side, after which it went into the laundry. Her boyfriend was a 1 towel a week person and she was beyond horrified. Personally I thought she had issues and her boyfriend should run.

What was interesting was the discussion in the comments section. There's a great divide between those who replace towels within one or at most two uses and those who don't. The people on the one-use side were especially horrified at the other side - one would think from their posts that the 1 or 2 towels a week folk were encrusted with germs most foul.

She would have a fit around here. We replace towels when it seems right - they don't smell as fresh. We're not so organized to replace all the towels on a schedule but instead they tend to revolve from bathroom to laundry to bath towel bin to bathroom on an as-needed basis. My concern with towels isn't what comes off a clean person but in terms of mildew when hung in a bathroom on humid summer days. So in the summer I tend to wash them more often than in the winter.