An interesting post on the Pros and Cons of conspicuity aids from the RoSPA Advanced Drivers and Riders blog:
http://roadarbloggers.wordpress.com/2011/05/09/the-pros-and-cons-of-conspicuity-aids/
Conclusions are in line with our own at this point – that, while there’s a subtle difference being made, HiVis and similar are not a panacea.