Unfortunately, no such effect for me. In fact, since i upgraded to Mountain Lion, i haven't been able to use kernel cache, so the boot times aren't as good as they could potentially be. That's sad, because the boot time of my i5 rig is already quite fast.
My estimates were actually a bit off. I restored 10.8.2, timed it, then re-applied the 10.8.3 update and timed again. Times are taken from the boot loader, not power on.
10.8.2: 35 sec
10.8.3: 14 sec
Very pleased, but also a little puzzled. If it helps, I'm on a x79 system. Windows boots in about 18 sec so I always suspected something was causing OSX to boot slower than it should. Oh well...
Seems this update has also fixed the occasional problems I would have with popping/ stuttering sound. Although it wasn't a consistent problem, it only reared it's head now and again. We'll have to wait and see.
So, all in all, better boot time plus a minor issue potentially solved, with no negative side effects discovered (yet).