Coming home the other night, with two sets of Ay-Ups on the bars and a Blackburn Flea on flash I still had a twat pull out into me on a mini-roundabout. You can light yourself up like a christmas tree, if the fannies don't look they'll not see you.
I am thinking of getting a helmet, not for any safety aspect but simply so I can attach one of the Ay-Ups to it, that way you can direct it at them when they're doing/about to do something stupid. I think that's the major benefits of helmet lights, especially really bright ones. They've no choice but to notice you.