I've been training chinese martial arts for a while now (bagua) ... here's some martial arts wisdom to be carried over to my BBing friends.
the stretching we do at the beginning of class has carried over to my weight training practice. my range of motion has increased, allowing more muscle stimulation during lifts.
i also hold less tension in my muscles, allowing recovery to be increased (decrease of lactic acid? more relaxed, enhancing rest periods.)
And for some reason, I'm getting bigger. I notice this in my traps and arms. Not only are my arms getting longer, my back is looking bigger.
Logically it makes sense. Holding alot of tension (which is increased by lifting weights) has a tendancy to make people curl into themselves. My shoulders were very tense, almost hunched at times. My traps have literally gotten about 20% bigger since beginning my stretching routine. I've really "filled out". This can also help your shoulder width to be increased.
Wake up people! Most of the pro BB'ers can do full splits.
I recommend if you want to include stretching into your routine, to do it everyday. It only takes about 15 minutes, you can do it a few hours before or after you lift. Even 5 minutes per day is better than 1 long session per week.
How to do it, mistakes to avoid, etc
If you don't want to get into the whole yoga thing, you can pick up a DVD. I practice dao-yin (daoist yoga) which is a form of Qigong (stretching + breathing exercises.) Go to amazon and read reviews for different dvds and pick one that sounds good. I don't even get on the floor ... they're all done from a standing position.
The main thing you want to focus on is stretching your core. That's where all of your organs are. Tension can cause your organs to be compressed, leading to health problems. Nobody ever died from "arm failure". The biggest mistake people make when stretching is focusing too much on the limbs and not doing whole body stretches. Think of it as "compound stretching". Everyone knows deadlifts are better than isolations.
So start thinking of balancing out your weight training with a stretching program. The results will really surprise you.