If I setup the networking manually for the install phase (IP, netmask, DNS, gateway, broadcast, etc) then this isn't completely carried over to the networking section for the installed system. The IP address, broadcast and netmask are entered correctly, giving the impression that the setup has copied all settings, but the (quite crucial) gateway setting is missing. It would be easy to miss this and end up with a system that boots, and appears to have an IP address, but couldn't do much with any traffic!
It looks like the installer was using the old-style /etc/conf.d/net line (gateway="eth0/1.2.3.4") to set the gateway instead of the new style (routes_eth0=( "default via 1.2.3.4" )). This is fixed in CVS. You can update to CVS by opening a terminal and running '/opt/installer/misc/updategtkfe'. Thanks for the report.