I have but I'm struggling to find a 'real' difference which would actually stop you from still getting on your bike. I find it quite strange that someone would stop riding their bike because they had to wear a helmet.
Spontaneity - which is why the London and Dublin cycle hire schemes have been so successful, Melbourne's has been a total flop and Mexico City is looking at repealing it's cycle helmet laws to encourage use of it's system. This is aside from the impression that cycling must be dangerous if it involves safety gear. Something that has been shown to be a major barrier to non-cyclists, especially female non-cyclists riding.
I also know two people in my reasonably small office who do cycle, but won't cycle to work (mandatory helmets on site) because of the helmet rules.
I don't read too much into the Australia example as it's about 20 degrees C hotter there than it is here so probably quite uncomfortable to do so for some, if anything here wearing a helmet would keep your head warm.
Today's high temperature for London is 25oC, Sydney's is 16oC. Just to check it wasn't a fluke for Sydney, Melbourne is also 16oC. Australia isn't uniformly super hot.
Whatever law comes in there's always someone banging on about how it infringes their civil liberties and such like rather than whether it will make any actual tangible difference to their life or not.
Amazingly enough, people usually bother to comment when they feel laws are going to impact them.
For helmet compulsion, however, there is a significant body of evidence that it is overall negative for population health, mainly due to the documented drop in cycling rates (if you need me to quote the whole Geffen position on this again in this thread I will) and the well documented benefit of cycling on overall health.
