Pretty good article in the Globe about SEVIS, the new INS system that I write software to help colleges use.
As of today, any time a foreign student drops a course, gets a part-time job, takes a medical leave, or changes his or her address, the school will have to file a report on SEVIS. Depending on their country of origin, some students may need to file with SEVIS if they leave and reenter the United States. And all incoming foreign students will need to be registered with SEVIS before they can receive a visa.
INS just announced a 15-day grace period so schools have a little more time.