I think it depends a lot on your hair's texture. I usually only wash once a week, and my hair looks better on day 3 or longer than day 1. My hair is coarse. There are a lot of fine haired wavies and even curlies who need to wash every day.

CG 4/13/2012
med-coarse texture/med density/low porosity
(2c/3a)
Clarifying: TJ TTT shampoo
Cowash: VO5 clarifying kiwi lime, Suave daily clarifying
RO: SN or Tresemme naturals, TJ TTT
LI: SN or VO5
Styling: Gels - HESMU, AAV; John Frieda & HETT mousse; TIGI Curl Booster, FX Curl Booster * Fan of plopping & diffusing