I know some of you got Nexus 7's for Christmas so I'll post this here:
http://www.droid-life.com/2012/12/27/fix-nexus-7-refusing-to-charge-try-this-trick/

I have never had this problem, but I see it a lot on G+ and forums. I think even our own Cirus had it happen once!

When my nexus doesn't charge I smash it

I had trouble with it at one point but I don't remember what I did to fix it. I think that I just let it charge for like a day and then it worked. I haven't had any trouble with it since.