I'd be willing to guess that most of you who have lived in China for awhile have made it to Kunming at least once, so perhaps a lot of this information will be redundant. The following is a general description of what life is like for an expat resident.
Kunming is the capital of Yunnan Province and is about three hours from Beijing or Shanghai by flight, or two by Hong Kong. The airport is not far from the city center and a taxi there from most places in the city will not exceed 40 RMB. They have begun construction on a new airport a bit further away, so before long this information may not be accurate.
Kunming offers several international flights, mostly to Southeast Asian cities. Recently, Air China launched a direct flight from Kunming to Calcutta, India, so convenient travel options keep expanding. Kunming is especially a good base for visiting Vietnam, Laos, and Thailand; there are consulates for each country in the city so obtaining a Visa is a piece of cake. You even have the option of traveling to Laos overland by bus (via Jinghong), though be prepared for a very long, uncomfortable (but cheap!) journey.
Kunming is famous for its mild weather, though the nickname "Spring City" is a bit of a stretch. The best times for weather here are from March to May and October and November, when Kunming is blessed with warm, sunny days and cool nights. The rainy season typically begins in late May and goes through September, but even in the summer it isn't uncommon to have beautiful weather. Kunming rarely gets very hot, and in fact in the entire time I've been here the temperatures never have exceeded 30 degrees C. You won't need to worry about an air conditioner, though in the winter time a heater is certainly nice. In mid-winter, Kunming gets down to about 5 degrees during the day and around freezing at night. It can snow here, but not terribly much.
An advantage that Kunming has over other Chinese cities is its combination of a diverse, cosmopolitan atmosphere and low prices. Yunnan Province is home to roughly half of China's ethnic minority groups, and so you'll very likely become acquainted with Bai, Naxi, Hani, and plenty more living in the city. Visiting minority groups in their ancestral hometowns is also easy: Dali is five hours by bus, Lijiang eight, and Zhongdian twelve. Xishuangbanna's capital of Jinghong is also twelve hours away, and there are plenty of ethnic minority villages in between these places.
Quite a few foreigners also reside in Kunming, usually either studying Chinese or working as English teachers. The area near Green Lake and Yunnan University is ground zero for Kunming's laowai population, due to its numerous bars, cafes, restaurants, shops, and art galleries. Within one square kilometer, you can eat Thai, Vietnamese, Xinjiang, American, French, Korean, Japanese, and Chinese minority food without spending an arm and a leg. For fellow barflys, there are quite a few bars and pubs that cater to a mixed Chinese/laowai crowd, so it's quite easy getting socially acclimated.
As for the cost of living, Kunming can be done quite easily on the cheap. Anywhere you might want to go will be a less than 20 RMB taxi ride, and the city has an extensive bus network. Rent, too, is less expensive than in most of the coastal Chinese cities, and if you stick mainly to Chinese food and stay away from bars you can live comfortably here on a very tight budget. Even still, a beer in a Wenlin Jie bar only costs about 8 kuai and even cocktails usually set you back 20 at the most. For those craving a more Chinese disco scene, the Kundu neighborhood and the area around Jinbi Square have quite a few places that stay up very late.
If you're wish is to study Chinese full-time, Yunnan University, Yunnan Normal University, and the Eastern Language Schools all offer inexpensive tuition for language study. There are also numerous Chinese students in the area offering Chinese tutoring for very little, or else looking for a language exchange partner. For those of you with a teaching background, it isn't difficult setting up a small tutoring business as the locals here are eager to learn or prepare for difficult English exams.
Some say that Kunming is beautiful, though to me on the surface it looks like most other Chinese cities. The locals, though, tend to be very friendly and there are many pleasant parks and outdoors areas for those who like to breathe fresh air. Pollution here isn't too bad and you won't lack for blue sky days, especially in the fall or in the spring.
If your interest is pursuing business or financial opportunities in China, Kunming probably isn't your best bet. Several people I know who have lived here have gone to Shanghai or Shenzhen in search for more lucrative work. Also, if you're worried about getting sucked into a drinking scene, Kunming can be a bit of a trap. But otherwise, I'd encourage most anyone to consider living here for awhile- you might stay longer than you thought
For more information, check out www.gokunming.com