I keep DSC on unless I'm really pushing the car; it's quite a nice safety feature. Yes, it does annoyingly kick in and limit what I consider perfectly safe driving, but it impressed me the other day.
I was taking a curve from one interstate onto another, one I know well and regularly take at 80-90. Well, about 20% into the curve, I see that CalTrans has been doing their usual stearling maintainence job, and a water main is shooting about 5 feet into the air on the left side of the road, about 60ft ahead. Absolutely _flooding_ the road about 2 inches deep for about a 15 foot strip. What to do? Well, I slow down as much as I can on the dry, but when I hit the water, the back end slips out and I start to tailspin. All four tires are soaked.
Before I get more than about 15 degrees into the spin, and just as I'm starting to compensate, the DSC kicks in twice, in rapid succession, braking individual wheels. The first breaking cancels the spin and put me into some kind of sideways drift, the second canceled that at exactly my current steering vector. All in well under a second. I was impressed.
So I keep the DSC on by default -- it can react faster than I can, and it's got a brake for each wheel.