I have seen this suggested other forum places but not one has implemented it. I think using a countdown would be more of a visual aid then having a set date which then users would have to look up a calendar or what not to determine how long that is. Some people such as myself are just that lazy we don't want to look at a calendar. The countdown would appear at the top or bottom of the first post in a font size of possibly 18 and in a red color. From there it begins counting down days, hours, minutes, and seconds.