I think change can be great if it's coupled with effective user management. On a site that people use daily, this means giving your users some advance notice, explaining major feature changes, and having a "how-to" page to show users how to use the new site. Lacking the above, there is bound to be some backlash as daily users find themselves stumbling around a site that they used to know like the back of their hand and, worse, with the very fabric of community interaction changed.