Of the JBs I have tried, I have asked myself, is this something I can't live without? So far, pretty much, no. I like the brightness buttons (but still forget they are there), and I find IntelliScreen X's easy ability to turn BT and WiFi off really nice - the FB, Mail, RSS, Twitter widget component I can live without (and have turned off except for FB, to conserve battery). Gridlock is fun, but in the grand scheme of things not critical. Pull to Refresh Safari is nice too - and should have been built in (actually, Gridlock, Push to Refresh, and one step buttons in the notification area all should be stock, IMHO ).
But I am seeing good battery life; much better now then when I first did the JB. Yesterday my phone was off the cradle for 12 hours, and I used Audible for an hour when exercising; I was at 74% when I plugged it back in. Can't complain about that, but I did not make any calls or texts yesterday. It was a light usage day.
Final verdict - is it worth being JB? So far, yeah. Will I lose sleep when I lose it for OS6? Probably not.