This is something that we are interested in as well. We like the implimentation that Evite has, where there is a summary of yes/no/maybe responses, and then a running log of who's responded, including a comment. We find that the comments particularly can help build interest in the event, and form an important part of the community feel of the association.
Since our association is mostly built around events, we would find some sort of listing of attendees extremely helpful. We agree with the earlier comments that an opt out would be necessary, either at the time of regestration, or as part of the member record, or both.