Well, today officially begins day 8 without any diet Coke/Pepsi. I haven't had any soda at all since last Friday(August 11). The first day was actually the worst--headaches and general crankiness--but it's gotten progressively better as the week progressed. I actually expected to be exhausted all week but I've felt fine AND I've actually slept better.
Don't think that I've been caffeine free though; I have been drinking iced tea, but not nearly as much as I was of soda.