Time per move?
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I don't. I would probably concentrate too much on a clock planning, and not on a game.
Every so often OTB, I will look at a clock and think 'I have another 20 minutes 'til the time control, or about 2.5 minutes per move,' but of course you would never restrict yourself to thinking in this way. Realistically, some moves will be performed almost instantaneously (e.g. recaptures when there are no tactics) while the critical positions will demand most of your remaining time.
Even so, a quick glance allows me to determine whether I am likely to be in trouble later on. This process only takes one or two seconds (just divide time remaining by moves, of course) and I always do it on my opponent's time, not my own.
If on the other hand you are talking about live chess, the time controls are probably too short to worry about these things, and you need your mind to be more focused on the game than your clock. (That said, always be aware of the time control you are actually playing.)
Exactly how you guys calculate(if you are doin' it) how much time you should spend your time for the whole game(secs/move)?