So this is becoming more of an issue to me..
First off I really like the my Nexus.. but signal issues are getting on my nerves..
I would say that it seems that my Nexus "can" get a good signal it just seems to fluctuate a lot.. when comparing dBm with my OG droid the OG will "settle" and hold a signal better (and with a higer dBm reading too) like at my home my Nexus will fluctuate from -93 to -75 on the same tower.. I have had the same results on a Completely Stock 4.0.2, Stock 4.0.2 with the updated radios, and custom ROMS with 4.0.2, and 4.0.3.. So it is more hardware than anything else..
Below is a picture of some thing I see WAY more than I ever have with other phones.. My Nexus would get a decent signal at the same location of the screen shots it just won't hold it at all..