Rapid Training

Hi-Vis aren't cool but in bad weather/poor light who cares - they work.
But they're a hassle to carry when you don't want to wear them all the time.

It's a beef of mine that waterproofs are made in dark fabrics for wearing when you most need to be seen.

The answer I've recently found is one of these H Belts. http://www.glo-marka.co.uk/gallery.php?cat=10
Great bit of kit.

Scrunches up small to stuff in your bag for pulling over leathers when it's getting dark or over waterproofs in the rain - a great aid to visibility without being an embuggerance.

Pay close attention to sizing - large is seriously large.
I had to return mine to get a medium, which works fine for my 42-44" standard chest measurement (in ordinary clothes, not leathers).

I have always operated on the principle that I assume they don't see me ...

Having seen people pull out in front of oncoming cars and lorries, I figure that even if I was dressed like a London Fashion Week <del>victim</del>model it would make not the slightest bit of difference.

Oh I agree absolutely -anyone who sees me and takes some notice is a bonus.
Although am I the only one to notice that this seems to be changing? In some areas particularly 'Think Bike' etc seems to be having an effect and a higher propertion of drivers seem to spot me and move over - not, of course, always in a helpful direction but the gesture is appreciated.

But if you take the principle of assuming invisibility to its absurd limits why bother with lights at all?
Especially daytime lights.

I use hi-vis in daily commutes in heavy traffic (M25 etc) and very poor visibility, because more people see me with than without and some is statistically better than none in terms of one's chances to live. That's why I like the H Belt because it is simple and unobtrusive but effective.

Hi-vis are also handy when you're coming up fast from behind with full beam: people definitely move out of the way a lot more. Even with a red bike, multi-coloured helmet and nothing that looks remotely like I could be an emergency vehicle.

I guess there's a difference to be made between active and passive visibility, if you see what I mean, lights belonging to the former and hi-viz kit to the latter. I.e. in the case of the former, they sometimes look / see you because of the lights: when one's driving for example, one's often alerted to the rapid onset of bikes from behind because of a glint in the mirror. In the case of the latter no one's going to see you in bright clothing unless they positively look, though as you say, if they're even half-looking then every bit of advantage helps.