Had JB since yesterday afternoon, still checking out some of the features but what I've seen so far...
Battery- I stay plugged in at home all the time, won't be going out until tomorrow for any length of time. Tomorrow will be the test.
Stability- It was a little choppy yesterday after the D/L, rebooted and it was smoother, but not noticeably faster, however, today it seems a bit more snappy with scrolling and page transitions. I may do another battery pull and reboot later to see if it speeds it up anymore. Really better than ICS at this point. It's a single core phone, it can only go so fast, I know.
Not Working- I haven't used all of the goodies yet, but the pinch to expand in the notification window only worked on a native screenshot, not on my GoSms app. As I understand it, the ability has to be written into the code of the apps, so maybe more will come online down the road. I really like the concept, hope it expands to other apps. The panorama camera works great! I have Google Cards set up but it did not present this morning like I thought it would spontaneously, I had to touch the search button for the weather pop up. Won't have any need for the public transit or flight cards.
Wifi, Data, 3G, 4G- wifi signal is stronger it appears. I was not aware of the toggle for weak signal and could not understand why 3G was preferred over wifi since I am in a fringe area with one bar. I thought Juice Defender was whackin out on me over JB until I found the 'weak signal' toggle in settings. Back on wifi this morning and it is noticeably faster than yesterday pre-JB. As for 3G, I still only have one bar and -96 to -106 signal. No 4G Wimax in my area, I will check that out tomorrow as well.
Performance- As I stated yesterday immediately after d/l it was choppy, almost seemed worse than ICS, even after reboot, not much smoother. But today, still on yesterday's reboot, it is much smoother and much quicker in transitions. I also hope it solves my random reboot problem that just seemed to crop up in the past two weeks. What was that about anyway?
Overall impression
It appears to be getting better as time goes on, but I was really not impressed last night with the features. It did not seem to be as big of an update as ICS was to GB. I guess I need to sit down with a list of updated features and try them out one at a time to get the full benefit of JB. If the performance keeps improving like it did from yesterday to today, I would agree that it was a successful and impressive update. I would think it would fly on a GSIII, I think the limits of JB on this phone belong to the single core processor and 512 RAM. However, I do love my NS4G, especially the form factor, and I look forward to the next Nexus debut, hopefully by December. I may just upgrade and pay the ETF for that.

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