Well, it's been over a year since I've pranged, but my experience is similar. I do hit my head on things occasionally off the bike - minor impacts. However, I've cracked several helmets over the years in hits that have had my full weight behind them. So yes, head hitting is more likely whilst riding than, say, surfing the internet. I have no idea if it 'saved my life' (I doubt it), but it definitely saved some hurt. All my crashes have been relatively slow speed though - I don't think I'd like to test it out in a more extreme collision.

All things considered, I think that the benefits outweigh the risks, even allowing for my concerns about the adequacy of the design.