Just got 10.8.1 and went for my short 3 + 3 mile test drive. It does seem to be better than 10.8, less turning jerkiness but still mini-hesitations when light turns green, car starts going but does a micro-slowdown and resumes, etc.
Seems to be improved at unprotected rights at stop lights, faster at making a decision to go, also doesn't seem to be haphazardly turning through unprotected rights with mini islands (pretty common for me with 10.8: car just seems to blow through unprotected rights without checking for cars? or maybe it already "knows"? I doubt it because it's done it with a nearby u-turner)
It also seems the visualizations are sharper, bolder, or just my imagination with the dark interface. I don't routinely drive at night.
I don't think I disengaged at all during the drive, mostly some minor accelerator pushes.
Could just be all placebo effect, and it's a pretty short drive.