There was a poster on here that used to use his Submariner (and no dive computer) when diving. Which I think is cool.
But as soon as you get into any tech diving, I am not so sure...
In general, though, my experience is that the primary timer is a dive computer and a watch is back up (on right wrist). I know guys who use mechanical dive watches for this purpose. But mainly quartz stuff like Aqualands which have backup depth guages. I have taken mechanical watches diving, but mainly strapped to my BCD in order to prove that a 30 year old watch can still cope. My back up is a G-shock.