Great thread! Quite the varied group we have here!
My main hobby now (or is it another job?) is my 5month old son.
1. Medicine, particularly medicine with limited resources and infectious disease.
2. Backpacking and bushcraft
3. International travel
4. Hurting myself with power tools (old boat and an older house)
5. Homebrewing, including homebrewing on the boat. (Drinking a homebrew now)
6. Macro-Economics. (nerdy I know, but it gets a lot less nerdy when your stock portfolio goes up and up and up...
Hobbies I used to do more of and would do more of if I had more time:
2. Shooting and reloading
3. Rock Climbing
4. SCUBA diving.