While most of my own use has been strictly recreational, I am strongly considering medicinal use. I have had asthma my whole life and have suffered to varying degrees depending on my living situation at the time. When I was married I had a cat (I'm allergic) but didn't smoke MJ regularly. During that time period my asthma became increasingly worse as time went on and I was eventually put on multiple prescription inhalers (albuterol, advair and singulair). Since my divorce and subsequent lifestyle changes (I'd only stopped smoking MJ regularly as my spouse did not smoke and was a bit paranoid about having it around), I no longer use the advair or singulair and rarely have need of albuterol (when I get a cold etc). This is despite smoking a plentiful amount of MJ on a pretty much daily basis. Ideally I will quit smoking cigarettes soon and will likely pursue using a vaporizer so as to minimize the pollutants inhaled.
I also had a pretty bad motorcycle accident in 2007 which banged up my left leg and hip. While I didn't suffer any broken bones, I still have a lump on my hip and experience joint pain after strenuous activity. Add that to lifelong joint pain and chronic back pain from my years in construction and warehouse work as well as a spinal contusion I suffered last winter (slipped on some icy stairs), and I have a steady need for pain relief. Maybe it's my mom's penchant for herbal medicine, but I'd much rather use MJ which is natural and clean than eat a steady quantity of chemical laden pharmaceuticals on a daily basis.