I guess my problem is that the groups I collaborate with contain people who aren't really able (or sometimes willing) to use sophisticated groupware, especially not if the use case requires them to use it in one particular way. My collaborative documents are therefore either restricted to small subsets of the group, in which case Google Docs works fine, or need to be easily findable by and open for read access only to people who don't have accounts in the groupware system, in which case really what I want is either Drupal or Mediawiki.