Bit of a loaded question...
I put 90%
... mainly because I use all the tyre right up to the edges, I use just about all the rev range, I accellerate hard when safe to do so, I brake hard when necessary and safe to do so.
I don't go silly on the bike, and I don't ride at 90% of my ability... that would be unsafe. I don't think using your bikes ability is about screaming around corners with your knee down etc - as in part that's down your own style and ability - not the bike's.