contrast seems to be a fixed pot thing for most designs I've seen. it does not like pwm (directly) for contrast. so I'll do the same, just let contrast be a small rail-to-rail pot with the wiper being the contr. pin. its a set-and-forget thing unless you change view angle a lot.
backlight is 1 pwm pin, direct, with a small series R but very small (less than 100ohms).
however, with 3 backlight leds (rgb, on some displays) you need 3 pwm pins! 
and things get harder, too, with rgb. dimming is trivial with 1 color but dimming with 3 colors and keeping the color mostly the same and varying only its luma? not easy not rocket science but not a simple for-loop either.
also, the pwm dimming is not linear so you need to have smaller steps at lower numbers (where the display is almost off) than at the top where yo can vary by 10 counts and still not see much dimming effect.
also, the pwm dimming does NOT seem to seep into the audio chain! that was a worry of mine. I did an rmaa test and the pga chip and display all seemed to be almost the same as the base noise level of the sound card test system, itself (m-audio firewire).
I'm glad we're WAY beyond the EL backlights and hummy/whinny inverters. this takes just 3 v for the leds and has no inverter or high voltage needed!