How much and how frequently should one walk during the third trimester?

When I was in my third trimester, I frequently walked around my office as much as possible and I brisk walked a lot. Even with a large belly, I wasn't one to waddle and would walk so quickly that others told me to slow down. I suppose it helped a lot because my labour was a very quick one, about 4 hours in between entering the delivery suite to the birth of my baby. I would say as much as you can possibly manage at a comfortable pace.