I have started taking dedicated and longer cold showers since last November (90 seconds or more) and they work great for me, although I feel they are much harder enduring in the evening than in the morning. I get so much energy and alertness from them, plus the little T-boost and increased circulation.
Most of the Indians (me also) take cold shower daily even if it is winter....so for us there is no challenge to participate.
I am on Day 5 now and it has been quite amazing. First of all, I've noticed that even with in the first few days, my tolerance for the cold has increased. My first cold shower was heart-stoppingly shocking. Now, on the fourth day, I can bear it quite well. I combine the cold shower with some exercise - before each shower, I do 10 pushups... and add one each day. So far I'm up to 15 pushups. I've found the added benefit of the cold shower is that I use way less water since they're like 30 sec long.