I've been running the second and now third leak for about 3 weeks now.
There's really not much difference IMO.
Good stuff:
Yes, there are more options in Settings.
Cell Standby reporting is fixed.
Transitions do seem faster. But I do notice lag using Apex launcher that wasn't there with ICS. I even tried setting Apex to persistent memory to no effect.
Not so good stuff:
I've noticed a slight decrease in battery life. I was getting 21 hrs w 2 hrs screen daily on ICS, with JB I get about 18 hrs w 2 hrs screen. And if you turn on Google Now, expect to loose another hour or more.
Yes, the 3rd leak may not be the final OTA build, so JB may be different when it gets to the i535.
Now I'm waiting on 4.2 with Photo Sphere! Don't care about gesture typing cause I'll always stay with Swype!