I go back and forth. I like the DG switch, but because it is made of a soft rubber-type compound it can catch on the holster material, slowing my draw a bit...In addition, the friction causes the DG switch to wear out over time. We have been working with Surefire towards a solution, and some guys have been testing a version that works very well (and that's all I have to say about that
I currently run my X300 without the DG switch while training. My duty pistol has a DG switch. We issue the light without the DG switch, so I run it the way we issue it (DG switches are approved at deputy expense) during most training. Ultimately I think the DG switch is a great addition that solves many tactical problems. The few new problems it creates are fairly easily solved.
When using the DG switch, one must learn how to draw the pistol without activating the switch. Most of the time, on a fast draw, it won't matter if you activate the switch, and you'll probably want the light on anyway, because bad guy already knows where you are. At the same time, it is not a good idea to have the light on all the time while searching, covering, assessing, etc., so the user must become proficient in releasing the switch while maintaining a solid grip. This is the biggest issue I see but is easily overcome with training.