When I was stock it would reboot....but now I'm rooted in gummy rom not one its been a week so we shall see!
CDMA Nexus. This has happened to me on a number of occasions. I was stock ICS for only about a day however and have been running Axiom v2.2 and v2.4. 2.2 randomly rebooted every now and again, sometimes after a phone call ended, other times when turning the screen on/off. I attributed this to overaggressive SetCPU settings (I had it down to 130Mhz and undervolted). Since moving to Axiom v2.4 (which comes with a different kernel) I haven't had a single problem with it.
I think it's ROM dependent as well as voltage dependent.
Got my VZ Galaxy Nexus on launch day. Stock ROM. I've seen probably a dozen or more reboots. I'd estimate 10 out of 12 were while using Google Maps/Navigation. Of those 10, a significant number have happened after switching apps (ex. to text/email) then switching back to Nav, and then boom within a few minutes.
Stock 4.0.2 - unlocked, rooted and modded few not-so-essential apks like Email (for corporate email). I experienced a random reboot for the first time last weekend, when I was trying out Wifi kill app. It worked fine initially, but when closing the app - my phone rebooted once, and got into a reboot loop - had to do a hard battery pull to get the phone stable again - I uninstalled the apk immediately just to avoid any future problems.
Other than this - I've never had any reboot issues with non-root apps.
Never had one here either. That's one of the big reasons the Bionic and the RAZR didn't stick around long with me. I don't like the instability. Been perfectly stable so far with the Nexus though.
I have CDO. It's like OCD except the letters are in alphabetical order, as they should be.