Yep, same issue here. The installer created an alias eth0:0 and assigned it the address of my router. I caught the problem during install and removed the alias, but it appears that mysql and some other processed may not have been started. After the installation continued, I saw some mysql scripts fail. That just can't be good... There really needs to be some exception handling in this install script.
I think I can suggest a way to avoid this problem. And yes, if you have it, packages won't download during the install, MySQL won't start, and basically you'll end up with a hosed install. The best thing to do then IMO is to reinstall Ubuntu and start from scratch.
Anyway... onward to the solution: When starting the install, select to configure the network manually. Give it some ip in your local network range. When asked to enter a range for the DHCP server, enter a 3-digit ip range that is not
in your network range. The virtual interface (eth0:0) would then be assigned the gateway address for that range, and it won't interfere with your net access.
Example: Say your router is 192.168.0.1. Assign 192.168.0.2/255.255.255.0 to the core network. Enter 192.168.1 for the DHCP range. Stir well.