In my field, coat and tie is almost unheard-of. It seems to have gotten worse in the time since I finished grad school, since back then many of the old-timers would at least wear a coat, but they are now retired, and what's left is a lot of people in stained t-shirts and jeans.
In fact, I just remembered going to a conference once where a group of us were discussing, quite seriously, whether a certain person at the coffee/cookie station during a break was a vagrant or a conference participant. He was, of course, the latter (and as it turns out somewhat well-known for provoking this question). To give you an idea of how bad this look was, we weren't exactly sitting on a high-horse in our t-shirt and jeans getups.