We are having the same issue when pushing to docker hub. It seems to be irradic and erred out initially mid-push of one of the images. Subsequent push attempts error out immediately. Over the weekend I was able to get one of them to upload after many attempts (lucky timing somehow?)
FATA Put https://index.docker.io/v1/repositories/thecompany/therepo/: dial tcp: lookup index.docker.io on 192.168.0.1:53: read udp 192.168.0.1:53: i/o timeout
Restarting boot2docker and even rebooting the machine seem to make no difference.