Did some tests, not entirely sure why it's doing this, but I can recreate the problem. If you have two network interfaces, one is connected and the other isn't. Set one to static and leaving the second one as DHCP, it will take 5 minutes to power up/shutdown.
However, if you connect the second NIC to a working network, or set it to disabled, the power up sequence will be fine.
This is a Ubuntu feature I guess. Probably just a coincidence it shows up in U7 and not before. Did you update your Ubuntu packages?
So the solution for now is to disable any unused network ports if using DHCP. Multi-NIC computers are still good though, in the future I'll add LACP (Bonding) support so you can aggregate your network ports to the switch. In your case if you have two NIC, you will double the bandwidth from 1 Gbps to 2 Gbps.