D-Lab Development has been oversubscribed by more than 200% over the past several years, and continues to be. In addition to doubling class size (fall 2008), we have had to come up with a mechanism to grant spaces for this class, hence the class lottery.
The class lottery is held on the first day of classes, and attendance is mandatory if you are enrolled in the class, since registration per se doesn't directly imply that you can take the class. After a presentation of the course, each attendee is asked to fill in a student profile. The results of the lottery are published before the next class, and that serves as the definitive list of enrolled students.
If you don't make it in a given semester, you may want to consider taking another class of the D-Lab family offered in the fall: