I have purchased many of these deals. Half off of one of my favorite restaurants? Yes, please. Half off a horse back riding trail? I'll take it. I've yet to waste my money by not using one. However, I can see how easy it would be to do.
So, my Groupon-Living-Social-Etc-Etc-Etc tip:
Write the deal and expiration date in your planner as soon as you buy it. That way you can see when it's about to expire so you don't end up throwing away a good deal.