I have been using a 1 day on with 2 to 3 days off for the last 4 months with success. I would like to point out that I am still very inexperienced with the idea of penis enlargement in general.
I have gained about a half inch in both length and girth using that routine of on and off days. When I started PE in 11-08 I had no idea what I was doing (not that I have an exact idea now). In fact in took about until late February to get an idea of how to exercise correctly and I am still learning much.
I started using a 1 day on 2 or more days off routine because I noticed that doing more days in a row resulted in a very “worn out” feeling in my penis. That is, erections were not as frequent and it seemed very sensitive to stimulus. Once I finally learned to listen to my body and back off a bit, things started to turn around. I am still trying to learn how to listen to my body and I believe that my routine and the amount of days on and off will be a forever changing process.