I too got the 5.1 overnight so we'll see what happens!
I don't have stress cracks but, I did drop it last week with the Rinke slim case on and both top corners of the case broke and the top left corner of my phone separated. I snapped it back into place and it seems fine but the shit thing is I have been complaining to Google for awhile about some issues and now, if they do send a new phone, they'll likely say the problems were caused by that.