My habits are such that I probably do 95% of my travel on the stream in an upstream direction, regardless of what I am fishing. For one thing, I'm almost always in motion when I fish and this means I leave a pretty significant sediment/silt trail in my wake. This matters, particularly on the smaller waters where I do the majority of my trout fishing.
There is a difference though between stream travel and fishing approach. I'll do what I need to do in order to make the fishing approach I think I need in a given situation. This includes making downstream presentations prn. So, just because I am working upstream does not necessarily mean I am always fishing upstream.
So far as the unwritten rules of angler traffic right of ways, etc., I always yield to another angler regardless of whether they are going up or down when we meet. Then, right after I yield, as often as not I'll just leave and go somewhere else. I get pretty misanthropic when I fish, unless of course I'm fishing with you. Otherwise, if I wanted to see other people, I'd go to the mall or something..
Regarding angler etiquette, I ran into something kind of odd when we were in the Midwest. There, at least according to some people, you were supposed to signal which way you went on the stream by parking on that berm of the bridge. On the upstream side if that is the way you went and vice versa. To be fair though, the handful of guys I ran into who actually thought this was a hard and fast rule were all loud mouth jerks in Cubs hats. More study is warranted..