Linux kernel have a bug that affects the default route for ipv6 networking. Adding an extra route manually can solve the issue.
Static routes improves overall performance of your network (especially bandwidth saving). They are also useful in stub networks (i.e. there is only one link to the network). For example, each LAN (located at different offices) is connected to HQ IDC (Internet data center) using single T1/LL/Wan links.
For example under Red Hat/Fedora Linux you can add static router for eth0 network interface by editing /etc/sysconfig/network-scripts/route-eth0 file. Under Debian Linux add static route by editing /etc/network/interface file.