Jeffrey Pfeffer in Business 2.0 writes in favor of deadlines:
So although setting a deadline may help rivals plot strategy, it can also get allies to act, create a sense of urgency when you need it most, and possibly even convince opponents that you’re serious. That’s why astute managers use deadlines to get things done.
My experience is that deadlines, especially self-imposed ones, are the key to keeping on track in managing your business. The problems arise when you have 25 things on your To Do List, all with vaguely defined wish-to-get-done-by dates, and none of them seem to get completed.