Man, do I ever go back and forth on this pickup.
I do really like the JB as an all-around pickup... great basic tone, hot but not too hot, sounds great for rhythm and lead alike, but the thing that keeps me from being totally satisfied with it is that I want the response to be tighter and a little fatter in the bass, and with a little bit better note separation at higher gain levels. On that last part - it's NOT a technique thing. At higher gain levels, notes sometime seem like they're smearing together during fast single-note passages. I've played a number of other pickups - mainly DiMarzios - that have a cleaner, faster sound, if you will.
I haven't been able to find a pickup like that yet. I'm told the Motor City Afwayu and the Suhr Aldrich come close though, but I haven't tried 'em as they are expensive.
I tried putting in an A8 mag in my JB for a while and that seemed to help a little at first, but I realized that doing that made the pickup too hot for me and the A8 mag added a slightly strident quality to the pickup that fatigued the ears after a while.
*sigh* What to do, what to do...