I'm not a fan either but I must admit I've taken advantage of offers presented to me in this fashion before. Some shopping sites will do this. If you've added items to the cart then go to close the page they'll offer an x% discount for you to complete the purchase.

However, I much prefer the sites that send me an email days later with an offer to purchase what is still in my cart but to do that you already have to be a user of those sites.