It's definitely a "yay" for me. I've been co-washing since I BC'd in June of '07. I'm a 4a with some other textures hidden throughout, but mostly 4a. I have little ringlets that people often mistake as locs or twists.
When my hair was shorter, I could co-wash everyday. It always made my hair soft and moisturized (once I learned to seal properly). I'm not going to lie. It DID take me a while to find a routine and products that were right for me, and sometimes, I still have to change it up from time to time due to things like weather and just general hair bipolar issues. I even overmoisturized once during my co-washing journey and switched back to shampooing for a while, which turned out to be a no-no, but overall, I've reaped more benefits from it than anything.
Right now, I co-wash maybe 1-2 times a week for a number of reasons. I find that my hair doesn't like to be manipulated a lot right now, especially while the weather is cooling down here. I don't have the time to co-wash everyday right now. I find that as long as I moisturize well that I don't need to co-wash as much right now. When summer rolls back around, I might start co-washing more frequently again, but who knows.
As some ladies have already mentioned, you'll have to try out different things and see what works best for your hair since no two heads are alike.