The comments system now runs as a script, along with all the others. All the old comments are wiped out (for this blog at least) but hopefully I should be able to move them back.
To swap to the new comments system without running changeCommunityServer (and wiping your templates), open Radio and then weblogData.root, and edit the variable weblogData.prefs.commentsPageUrl to change /comments to /system/comments.py.
