I have made this new course block that I think may be quite useful to alot of people.
It displays a customisable countdown timer of the enrollment period left for that user. The display is quite customisable, and there it has been designed so it is as easy as possible to bring inline with your theme with css overrides.
As extra functionality, there is a cron on the block that sends out customisable warning emails to the students advising them that they only have X amount of days left in the course. On top of this the cron also checks for students who have passed the course in the last 24 hours, and send them a customisable congratulatory email.
See the link below and let me know what you think of it.
I am sending it for approval so it can be added to the Moodle plugins page.