Mm. "Should you study Chinese?"
If you are just passing through then my opinion is 'no' you shouldn't unless you have a passion for learning languages. That being said, 'studying' doesn't mean you have to go to any school. You can study slowly and at your own pace. As previously mention, it depend on your goal. Some people are gifted in learning languages and some are not. I don't think people should belittle other people because they have been here awhile and are not that good at speaking, writing or learning Chinese. Kunming is not an ideal place to engage in 'putonghua' because they really don't speak it well here. Despite that I think an attempt should be made to get to a least a basic level. My 2 cents. Ha..ha.
@Liumingke: Kunming may not be an ideal place, but then different situations motivate different people, and these can make a lot of difference. I was a disaster in secondary school and university when having to learn a foreign language (Spanish, a relatively easy one, at least for native speakers of Indo-European languages). There were virtually no native Spanish speakers in my area, I really hated language study, especially those damned language laboratories where you're asked to converse with machines, and I very early on concluded that, although I was a good student of other subjects, I was unfortunately an idiot when it came to foreign languages. Then I got interested in China and realized, if I wanted to pursue this interest, I was going to have to learn this seemingly impossible language. I went to China to study, found that I really wanted to be able to communicate with people, took classes and was honestly surprised to find that I am perhaps a little better than average as a language learner.
Different methods for different people, but also a matter of attitude and motivation. Knew a guy who'd graduated from Oxford in classical Arabic, could handle the Quran, poetry etc. - went to an Arab country as an English teacher, found that daily spoken Arabic is quite different, never learned to speak it, remained living in a foreign bubble.
Should you study Chinese? in my opinion, YES. It makes your life here easier, because most of the local people don't speak English, such as taxi drivers, street vendors, those working in the management office of your compound, the fuwuyuans in most cafès/bars/restaurant. Yes, you can carry your dictionary around, or use the newest iphone app... but I believe you'll get tired of it.
Speaking some Chinese will enable you to interact with locals, and will help understand their culture and environment. You need that if you want to get out of the "foreigner's bubble".
For what concerns work, if you have a job outside teaching, you definitely need Chinese (at least in Kunming). And for what concerns teaching, well, I believe that being aware of the process of learning a foreign language, as well as the frustration and hard work required to achieve fluency in another language definitely helps you understand your students better. Knowing something about Chinese grammar, you can often predict their mistakes, and understand why they always get the same things wrong. And while you are learning, you are "on the other side of the desk", so you can try out learning techniques and strategies yourself. And as someone previously said, it's a great training for your brain.