It really depends on your head of hair. I used to co-wash every day when my hair was short (TWA status) with no problems. When my hair got longer, I stopped doing it so much because (1) it's time consuming and (2) my hair really started liking low manipulation and protective styles.
Last relaxer: August 2008
Big Chop: December 2008/January 2009
Blog: Alice in Nappyland