I'd argue that occasional movement is appropriate - if you don't move at all, you create an issue with line-of-sight that a student can use to cheat. However, pacing around like a caged lion is not the answer. I generally move from front to back to sidewall every once in a while. the back however is definitely the best place to observe, particularly if you are administering a test on computers because you can usually watch progress bars on the screens.
