Ok, I'm new to Service Electric/ProLog and was furious at the performance. However, searching the Linksys forums (that's my router) I saw some info on changing the MTU setting.
After playing around, I found that setting the MTU to 1200 has made my one-way cable modem function 1000 times better. It was stalling on downloads, DNS lookups and dropping me from World of Warcraft. With the new MTU, it's running without a hitch.
So there is hope.
Hint: Make sure to reset both your router and cable modem after making the MTU change.