Short answer: it has been beneficial; I mostly use the breathing exercises as necessary. I don't make as regular a habit out of them as I probably should.
Here is the
audio CD I used to learn different exercises. The relaxing breath is probably my favorite...works every time. Because of learning about the breath, I am very aware of my breathing patterns and I think that I have made deeper diaphragm breathing more of a habit.
Stretching? Always. I know Brian G. and Bill will have a problem with it, but I seem to need to stretch more as I get older and so I'll follow a regular stretch regimen in the shower in the morning as well as post workout, and if I've had a particularly tough workout, I'll break out the Homedics massager and work myself over pretty good. I find it definitely leaves my muscles feeling more refreshed the next day. Probably just blood flow and waste product removal.
Bryan, do you know much about stretching/massage and the lymphatic system? Seems to be a hot topic I keep reading about these days.