Not sure how much of this has been covered in other threads since there is too much in this forum to read it all, but my GNex has not been the same that it was the first day I got it. As with each smartphone I have had, once I installed apps and changed settings it now lags and occasionally reboots for no apparent reason. It's done it a few times that I have noticed but never when I was actually using it, so far. I haven't seen this mentioned yet, but when using an app and then switching to my homescreen, the homescreen is blank except for the app drawer button. Then the icons load after anywhere from one to five seconds. It does it a lot after using the stock browser, but occasionally after using other apps too.
I am using the stock ROM but the phone is rooted.