I (Andrew) been including cold showers in my daily routine for a while now and I feel like its time for a little retrospective.
First up, I have modified my shower routine. I was starting out hot, soaping up then switching to straight cold reasoning that the need to de-soap forced me to get under the cold. This routine worked but wasn't terribly pleasant. I've now modified my routine. I start with a regular hot shower and at some point start to slowly dial down the hot water until the water is more or less straight cold. I say more or less because sometimes I make it all the way to straight cold, sometimes I do not.
The memory of the highly stimulating if somewhat jarring effects of the first few cold showers is still very clear however those effects seem to have faded over time. I guess I've become habituated (my big word for the day). Now a morning cold shower is like a nice cup of tea instead of a double espresso.
While the wakey wakey effects seem to have faded I do find that I am somewhat addicted to the cold water routine. I'm not sure exactly why. All I know is that even when I get into the shower thinking "not today" after a few minutes I find myself repeating the now well worn routine of slowly turning down the hot water.
I cannot quantify the fairly questionable health benefits of this routine however I suspect that I may have developed a lifelong habit.