Convenient Advertising???

I recently ordered a pair of boots from Urban Outfitters a couple of days ago. Since I have ordered them I have noticed that the same boots I just purchased constantly show up on the side advertisements of whatever web page I'm on. Before this had happened I enjoyed looking at the side bar ads because I thought it was kind of cool but now I find it quite creepy. I bet this has happened to other people as well and I'm curious to know what they thought about it. It would be better if they didn't show the exact thing I ordered and instead showed something similar in style.