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in for four steps, out for four steps
That's pretty slow breathing!
I'm often aware of breathing when running at a harder pace, not so much easy pace. I even use it for pacing tempo runs; if I can maintain 2-in, 2-out without resorting to 2-in, 1-out, this sort of vaguely corresponds to marathon pace or a bit quicker. I might allow myself some leeway when tackling a hill, but I think this is reasonable practise since I think it's OK to do so during a race in order to maintain good momentum, on the basis that you can get a bit of a rest aerobically on the downhills.
PhilPub-
I've run to breath count (alongside hr)for as long as I can remember in road & xc as it correlates well to hr and makes running on feel without hrm much easier.
6 as 3 steps in/out (always LRL in RLR out) was my default even for steady runs but I've recently switched to 5 in 5 out (starting on left foot still) to ensure my easy pace doesn't increase gradually as yoshy described.
5k race effort will start at 3/3 then hit 2/2 sometime during as the hr ramps up. I'd have to pay attention more to know what's going on in the last few hundred metres, all sense is obliterated by pain usually.
rhb
Regulating my breath helps me for easy runs: in for four steps, out for four steps.
I generally have no pacing discipline when alone though, I either run hard til I'm tired, rest, then run hard again or try and do a slow run and end up thinking "omg I'm feeling good today" because I've been running slowly and gradually speeding up.