Every 4 or so days. My hair changed while pregnant and Fructis just wasn't doing the job. Since switching to Tresemme I can go a week. lol.
Funny you say that because I changed to Tresemme and I had to wash my hair more often and it made my hair very frizzy and static different for everyone I suppose.

I used to get really oily hair and wash everyday, I now wash twice a week and never feel that it is really oily (not like it used to be every morning), I had to train it though and in the beginning it was horrible! I also have dark hair but mine is very straight naturally.

I used to use conditioner but only on the tips to avoid extra oil on the scalp, now I don't use conditioner at all.