Along with the functionality to use both paypal and enrolment keys together (should be fixed in Moodle 1.4.3) , I would like to suggest that Moodle should have a feature (I'm not absolutely positive that this is a new feature) where the student could select either paypal or enrolment key (a single web page with both options) before enrolling in a course. This functionality would cover the scenario where a student has prepaid for a course through some special arrangement (i.e. businesses or schools paying in advance for a group of students) or is allowed into the course for free. The student could just use an enrolment key (provided by admin or teacher) to enrol in the course. This feature would cut down in administration time by allowing students to automatically enrol in courses without the admin or teacher having to perform this task manually (however, manual enrolment should always be an option). They would just give out the enrolment key to this group.
Please let me know what you think about adding this feature (if it is a new feature, maybe enrolment is suppose to work this way) to Moodle.