I neglect serious stretching, too. I do it, but not as frequently as I feel I should. However, I do try to do yoga on a recovery day 1-2 times a month. I do TurboFire's Stretch 40, ChaLean Extreme's Recharge, P90X's Stretch X or Bob Harpers Yoga for the Warrior. Since I have discovered Cathe, I got Stretch Max, Yoga Relax and Yoga Max, and I have been doing even more stretching. Stretch Max in particular makes it easy to tack 20 minutes of stretching to end of a workout. I also like to add Stretch Max or one of the Yoga Relax/Max 30 minute premixs on to the end of one of Cathe's 30 minute HIIT workouts.
I guess my point is, I am trying to fit it in anyway I can. Once or twice a month I will do a long flexability/yoga routine. I'd like to say I do one of the shorter ones every week, but in truth, I do one every other week. I'm just grateful Cathe has longer cool down stretches than other trainers. I feel like I am getting some good stretching in from her workouts.