I've known a lot of folks in various capacities: one lived in Shanghai for 8 years teaching, another teaching in Shanghai for a year and then Fulbright for a year (spoke Mandarin), Taiwan, a guy and his girlfriend in Guanzhou (rural China), Thailand, and several in Japan and Korea. I visited several friends doing this in China and my co-worker's brother started his own business in Prague (a long time ago).
I also know a shitload of Returned Peace Corps Volunteers and other folks working in different capacities (Fulbright, etc.) in education and development throughout Africa (Liberia, Rwanda, Malawi, Lesotho), the south pacific, Malaysia, Nepal, Philippines, etc.
My general observations (different personalities and cultures, so grain of salt:
-As Nards said, it ain't some big adventure. A world of difference between teaching English in a major asian city and the Peace Corps.
-People in Japan and Korea were generally happy with living conditions and pay compared to China
-Folks in Taiwan are happier than those in China
-Of those in China, the ones in more rural settings were more content
-Contrary to what Pangloss said, those in developing countries were the happiest, though I do know several that were robbed: including a priest that had been robbed 10+ times in the Philippines over 10 years and 3 people who's house was robbed in Liberia as they slept (the government reimbursed them). I suspect, however, that this has more to do with personality types, as well as the level of responsibility and variety of work (helping out or managing several different initiatives vs. teaching day in day out
-If you get a girlfriend in China, she will be Korean or Japanese
-The nicest living conditions were those living in dorms in China. They have several new universities w/ brand new buildings, so the digs were nice... especially in more rural settings.
-Married couples loved it. Of the unmarried couples, the guys normally wanted to stick around, while the women wanted to go home. I suspect this is based on two things: 1) Women get treated like shit in a lot of non-western countries, 2) The guys wanted to try and bang folks (especially true of those on college campuses
All in all... it depends on your goals. If you want to try it out and make a little money, it sounds like Korea and Japan are your best bet. If you really want to make some money (with risk), I'd say Africa is where you want to look. If you're looking for adventure and rich experience, you're probably better off in a more developing setting. If you just want to teach, it's not worth it; here in the states, there are several opportunities to teach in rural communities such as Alaska or indian reservations, that will pay a lot better (American pay + education if you pursue that), or Teach for America if you prefer urban settings.