Personally, I'm one of those that come from a CS background, and so I use the mouse for pretty much all movement whenever possible-- I'll often just hold down both mouse buttons if I need to run for a short distance (and anything longer gets the run lock key from me). I also think that circle strafing is pretty much the best game mechanic ever made, but I know that there are those who disagree with me-- back when I worked at Gamestop, one of our employees there just couldn't seem to wrap his head around the fact that he should turn and move at the same time, and as a result just got dominated in our Halo matches.
But habits are a powerful thing, and so keyboard turning is probably around to stay. I won't go so far as to say that fast-turning with a mouse is required to be a good player, but certainly that kind of reflex is required to be a really great player. So keyboard turners, pick up that mouse and start looking around-- you'll thank me later.