I just got 10 RP B+ and all of them have the same problem, which I believe it is manufacture related. USB and Ethernet don't work. I doubled checked power supply (5V stable, 2A), kernel and fw are fine (I've used the same version for months). Since it happened with 10 RP, I'd say there was a problem with the whole batch.
I've read about this problem (http://www.raspberrypi.org/forums/viewtopic.php?t=5766) and it appears to be with the clock not getting to LAN9512 and thus, this doesn't have an easy solution.
Since all I read about people with this problem is from 2012, I'd expect RP people to have fixed it by now. Does anyone else encountered this problem with B+? Is there any solution that doesn't require sending back the RP or the need of a NI Freq generator?