• On that note, it would be nice to have a report (I guess it would be in the
  user's profile) to show pages which the user has been involved in
  which have been recently modified (would also make a good RSS feed).
  ie "Show me pages that I've edited / commented on which someone else
  has modified in the last 7 days".

Not sure how efficiently we can query all these things - perhaps have
'association types' in the system that have to be able to get all the
content that someone is associated with in one SQL query?

interface UserContentAssociation {
public Set getContentEntitysAssociatedWithUser(User user,
DateRange validDates);
}

Then you have 'commented', 'edited' association types, which should be
able to get the desired content objects in one SQL query?