Seats in all elective classes at Wharton are allocated through an online auction (using points, not dollars). Basically, seats go to those who are prepared to bid the most points. While students joke amongst themselves that it the most complex solution to a non-problem every invented, it does ensure that each seat goes to those who actually value it the most, rather than those who put their name in first, or got lucky in a random ballot.
Basically, you will be able to get a seat in ANY class you want, but not EVERY class you want - it forces you to think about the trade-offs you are willing to make.
Also, even for very popular classes, you can typically pick up a seat in a less popular timeslot, or the same class by a different professor, much more cheaply.
btw, Professor Diamond's class is awesome, and worth every point I paid for it.