.
My wifes been on about getting a helmet cam for some time. generally ive shied away.
Guess it depends on how often you cycle and the frequency with which you meet problems.
When I was commuting daily in Birmingham I'd have had one because the standard of driving was aggressive and frequently dangerous whereas the intensity I'm meeting it now in the country simply doesn't warrant one.
There again, I've stopped wearing a helmet and don't see the same value as having it on the bars. It'd never catch the aftermath.