I tried disabling JD under 602, and my battery life went down faster than what I recall under Froyo. Sorry, can't compare 602 to 596 accurately, but I believe GB may not be the only reason... could be 1 or more of my installed apps.
Phone Idle and Cell Standby are the culprits. I need to use JD to get any kind of decent battery life out of this phone. Nothing like turning off data except for short bursts at 30-min intervals.
Sent from my unrooted DroidX using DroidForums app.
My experience thus far is that it doesn't seem to be making any noticeable difference either way for me. I don't have that many apps that push data, no live wallpaper, and very few widgets so, I may not have been using much idle power to begin with.