If you mean little plastic mushroom things then yes, they limit the power to just over 100 bhp, the French being the only EU country who took up the 100 bhp limit for bikes. So if you buy a new 1600 BMW for ex it will have only 100 or so bhp, rather than go for a power to weight ratio limit, daft sods!! I think this is to be repealed in a couple of years though.
I think this is the only restriction to power, you might like to check the lights and the speedo too though
Tommo