MTB Drop Bar:
http://mtbtires.com/features/bikes/why_dropbars.html
http://twentynineinches.com/2010/03/...-off-road-why/
Bar width has lots of factors: head angle, trail, fork length, TT length, stem length, desired attack position on bike, and your size.
Good intro about bar width from RC
I suggest starting w/a wider bar & moving grip/levers in/out until you find your most comfy width, then cut.