I've been carrying a Surefire Stilleto Pro for a few months now and it sits in my left front pocket just like a pocket knife would; it feels basically the same as my Spyderco Para 3 I have clipped to my right front pocket. I greatly prefer it to the round-tube lights I've had in the past, including the thin AAA Streamlights and single 123-A Surefire's.
I haven't had any issues with the Stilleto Pro coming on in my pocket, unless I hit the rear button (I changed the clip to carry the light button-up; I find it easier to draw and activate the 5-lumen task light that way and I like not having the bezel exposed). I had a first generation Stilleto and I had more unintentional activations with that light than I've had with the Pro.