Another recent article on the charges:
http://www.insidehighered.com/news/2007/08/06/rider
The article mentions activities besides the drinking, including push-ups and sit-ups and a scavenger hunt. The article indicates that those activities weren't required of the pledges, but the older members wanted the pledges to participate in them. It wouldn't surprise me if there was moderate to strong pressure for pledges to take part.
Reader comments following the article seem to run the gamut of likely responses.