I only lowered mine about an inch front and back... I noticed (and my passenger noticed) that I'm leaning a bit more now when I turn (unless it's all in my head - but it was in hers too i guess... could also be confidence in the new rubber 8)).
Also, I hear that if you lower the front just a tad more than the back you get a more sporty feel. A local guy who used to work as a mechanic on a yamaha race team said they would lower the front ends on all of their bikes for better handling.
I can't vouch for this yet, though, because I still have clubmans, so I am only able to lower the front end an inch.
*Edit: some of the race guys over on caferacer.net told me to lower the front the width of a penny at a time to be careful... seems like horseshit but maybe on a track it'd make a huge difference.