RhinoFish - 8:58 pm on Dec 5, 2010 (gmt 0)
yep, on the display network, you can use a negative remarketing audience to accomplish that.
"For my campaign, it doesn't make sense to advertise the site to people who are already using it."
rarely true, imo. you may not want to show them the same messaging, but your past buyers are likely great referrers...