I never was, but my GF was one time. Not being very experienced and getting pumped out and scared she placed the first cam she grabbed, a BD .75, completely tipping it out in a little divot on the sides of the crack. She fell and it held.
Also, I've placed cams passively, in huecos where the cam could go in then open but couldn't come back out.
They are nice, especially in smaller sizes. A couple of times, I've placed things super tipped out and had cams walk where the cam stops would have been useful.
Not me. However, I had a number of cams get messed up before cam stops. The old friends used to easily (relatively) get pulled beyond their wire stopping points. You could get them back, but they never seemed to work as well again.
I know BD cams are rated for passive placements, but I don't think anyone else is, the ol' double axle. I don't feel like simple cam stops would hold a damn thing. I think DMM might have ratings for their cam stops, not sure though.
Edit: DMM rates their cam stops at 10kn, I'm surprised that they are that strong, strong as a nut...
A (newer) WC Friend's cam-stop strength is nearly equal to the strength of the cam. On the larger units, they are rated from 11 kn - 14kn. Still, Camalots reign supreme.
not for long? DMM is coming out with a double-axle cam, the Dragon Cam. with a name like that i fell like i'd HAVE to buy one. i climb on DMM's 4CU's currently and really like them - i'm very interested to see what these mythical beast cams are like.