<Snippet> Make a point to let customers know they have to act fast, or they'll miss out. The fear of being left out or left behind is a basic human motivator that can be triggered pretty easily. The trick is to actually let your customers know an offer is limited in some way. Here's how to create a powerful limited time offer.

Read more (http://www.smallbusinessbrief.com/articles/copywriting_and_website_content/002461.html)

This is a good article and so true! People are procrastinators! Give them something...and they still wait. I know this by experience. We have an in-house drawing every day. $ 10.00 off the next time you dine. Only those who have come in that day are in the drawing...so the chances are great! We know the people want to return....(or why would they put their name in the drawing?)...yet....they procrastinate. When we started the drawing..we thought they would rush right back in...and some did. However....as the days went by...the coupons started adding up. When we realized without a deadline to use them...they would take their own sweet time in returning..we put a "must be used within 30 days" on it.

Good example. Make sure that your expiration date is very visible or you'll defeat your purpose of creating urgency. If they can't easily see on the coupon that it expires in 30 days, having a "use by" date won't have any effect.