Assuming you meant the countdown timers that always count down from the same starting point every time you visit a site: they are misleading and downright annoying. I'd never use one. If it's a real countdown, then it has its merits.
I've got a client who has one on one of their sites but it's not dynamic as it only displays days and it's referring to actual dates when prices will change.
Hi: Countdown timers can work to create a sense of urgency when used properly. Make sure that the timer doesn't start over each time the eprsoon opens the email or source. If the time starts all over again people will perceive it as a fraud. Don't put a countdown timer on everything you send out though. Dan
I don't see the purpose of it, really. As someone posted, it is more a waste of resources for your site.
A countdown timer is the best way to demonstrate that a sale lasts for a limited time, a nonverbal way to tell customers: soon a carriage will turn into a pumpkin and the price for that new bag will become huge again. You need to hurry. Urgency is one of the best decision-making factors, so why don’t you use it to encourage a subscriber to buy?