A week or so after updating to Intrepid on my work desktop, I started experiencing really slow internet connections. (around 100k/s). Tried a different network port - no change. Booted into windows, and got 2M/s. After perusing the ubuntu forums, I found this solution:
edit /etc/sysctl.conf and add_ net.ipv4.tcpsack = 0 net.ipv4.tcpwindow_scaling = 0This turns off IPv6, which seems rather heavy-handed, but disabling ipv6 in firefox alone didn't fix the problem. I suspect that it was the result of a change somewhere in the school's network, but dealing with their IT dept is like banging your head against a wall repeatedly. Hope this can help someone else with the same issue.
edit /etc/modprobe.d/aliases to remove_ alias net-pf-10 ipv6 and add_ alias net-pf-10 off alias net-pf-10 off ipv6