I first discovered ice dipping about a year ago, via The Tendonitis Expert, in one of my many quests to cure my tendonitis while constantly dancing, moving, and sprinting for airplanes I was about to miss. I was not new to ice treatments, and was already icing my tendon with an ice pack for twenty minutes after activities likely to irritate it. Despite this, I'd wake up the next morning and barely be able to walk, let alone dance. Ice dipping (along with eccentric calf drops and massage) is what finally got the pain to a manageable point. Basically, I dump 10-15 frozen water bottles in a large bucket that comes up to my knee and fill it with water. I dip my leg in for 30-60 second and remove it. I wait about 5-10 minutes and come back, and repeat over about a two hour period or until the water melts in the bottles or I have to go to bed or whatever. Theoretically, this works because the ice draws the blood out and then new blood rushes in when you take it out, over and over, which is what your tendons need to heal. It is especially affective with a tendon like the achilles that has a poor blood supply. Whether this is true or not, I have no idea, but it works like nothing I had ever experienced. After one week of ice dipping last summer, I could dance again. I now mostly use it as a preventative measure (and have learned the hard way that I need to not skip it, although a day or two without is fine).
My cats, of course, enjoy drinking from the bucket and seem to have developed quite the taste for ice water.