I'm using OS X 10.9.3 and for some reason adb no longer detects my galaxy nexus running Android 4.3, but it does detect my old myTouch 4G running Android 2.3.4.
I'm guessing that this issue may have something to do with my Android SDK's being updated, but I can't say for sure. I just know that it worked one day and stopped the next. I've toyed with the Galaxy Nexus, confirming that USB debugging is on and in MTP mode (though I've tried it in PTP mode as well all with no luck. ADB doesn't detect my galaxy nexus. I've come to believe it is most likely an issue with updating Android SDK's on my macbook pro, rather than an issue with the phone's settings, but I'm open to suggestions.
I have not installed easytether and no kext exists to unload as suggested in this thread: Android adb (OSX Lion) does not recognize Galaxy Nexus, Jelly Bean