Runner's Forum: Breathing patterns

I've been running half-marathons for about 5 years, and during that time I have found breathing patterns very useful.

I.e. breathing in a sequence with my foot falls, matching how many footfalls for an in-out cycle, which becomes unconscious after a while, but I have found VERY helpful in improving my distance and times, and my happiness during long runs. (I have been known to smile all the way round a half-marathon)

When I started (running a mile) I ran 2 in, 2 out, then for a long time, I used to run with a 3 in, 3 out pattern, but more recently (and especially over long distances) I find myself running with 3 in, 4 out, or even as much as 4 in, 5 out. (9 foot falls for a breathing cycle)

Also, it is interesting to notice the difference hills and speed make to the pattern. (but this can be pretty impossible to do while listening to music, so I don't usually take any ;o) 

Does anyone else use these patterns? 

If so, what breathing pattern do you use? Which is best for you in what situations?

Is there any science to this?

It all depends on my mood really! I normally find 3in-3out to be most comfortable, but having said that, it normally goes to 3in-4out after a couple of miles