I have the latest EOS Utility. Its working fine. My 40D works fine. When I connect the 5D, it sometimes get hung, sometimes it downloads a few photos and then gets disconnected..Same thing happens with Adobe Bridge too. may be a camera issue. I am going to return it and exchange for another one.
The ~30 Mb file size from the 5DIII is presumably larger than from the 10.1 Mpixel 40D. Could that be the problem? Downloading is slow on the latest MacBook Pro top of the range.