1 finger on the brake and 2 on the clutch during spirited riding or while in traffic. My 1 finger on the brake is just strong enough to provide sufficient braking without hesitation. I have tiny fingers so adjustable levers are a must.
I do it because I use this technique for mountain biking. It only takes one time for you to be losing control and lifting all your fingers (not thumb) off the throttle/grip to grab the brake when your wheel hits something and shifts the handlebars right out of the grip you didn't have.
Go hit up the parking lot, throw out a couple markers, do some tests of you own and let us all know how you feel about it!
Current Bike: 2010 KTM 690 Enduro R
Previous Bikes: 2009 F800GS / 2010 Triumph Daytona / 2004 CRF450R - Supermoto / 2007 GSXR 750 / 1991 Yamaha XJ600 Secca II