IMC holders will crucify me, but I read about them all the time....... in the monthly AAIB reports. IR holders would concur
I expect you'll find that most accident reports - well the weather related incidents anyway - either come from IR holders or non-instrument rated pilots.
I personally know (knew) 1 IR holder who flew into a mountain during an instrument approach. I don't recall any specific weather related accident which was due to someone exercising the privileges of an IMC rating, although there may have been one or two where the pilot was attempting not to break any rules by trying to remain "vfr"....although they probably could have continued safely in IMC...