I had my Nexus replaced about two weeks ago because the random reboots and lock-ups got so bad that the phone was unusable. Now, i've got the mic cutting out on every call. At first it was after about 20 minutes, then about 10, and now it's as soon as the call connects. The other person can't hear me, but I can hear them just fine.
Also, it doesn't matter if I'm using the phone normally (held to my head), using the built-in speaker phone, using a wired headset, or using bluetooth (headset or speakerphone). It does the exact same thing no matter how I make the call.