Barring getting dirty or sweaty, I only shower ever two, or sometimes three days (Depends on my hair, I use it as a measuring guide) as I don't smell, don't sweat very easily at all, and don't suffer from bedhead (One good run with a comb and I'm set)
Most people balk when they learn that, but Honestly, I have people compliment me on my smell. When my hair starts to get a little stringy/greasy, I'll take a shower at night, and I'm set.
Of course If I've got plans, got dirty, ect, I'll usually shower that night instead.