Students and teachers are locals. Tourists - people from other countries here for a few days will opt for the taxi's. I may be wrong but I can remember when I was in China a few years ago there was a lady afraid to go on the elevator without her husband. (I came to China alone as a tourist) He wanted to walk down - so she got off the elevator and walked down with him. Tourists from smaller cities or from countries without subway's will be leery to try. Tourists from cities with subway's would be more willing to try.
I dunno. I'm a student/teacher and often a tourist. That makes me a poor tourist, and I'll stick to the subways and buses wherever possible.
When I first got to Beijing (about 2 months ago) I took cabs frequently, but now it's probably been a few weeks since I've been in one. Beyond their being a luxury, my stomach isn't quite strong enough for the ride. Roller coasters, rock climbing, rappelling, etc., I can all do, but Beijing taxis are something out of this world. One driver I had actually hit a girl while we were racing through Sanlitun. He'd mostly slammed on the brakes in time, and she was only a bit shaken, but that was far from a thrilling experience. Another driver I had asked about Chinese public alcohol consumption laws assured me that I could drink on the street without a problem, explaining to me that he often stopped along the road to drink with some buddies when he took his breaks.
I've switched to a bike. I have a helmet and lights (look at the funny laowai!), and biking has its own thrilling set of dangers, but I'm psychologically better suited to being in relative control of my fate, I think.