It would be nice if Adium's behavior when attempting to use an out of date Xtra was better than just silently failing or crashing. I'm envisioning something like Firefox's extension versions, or Shapeshifter's handling of themes that haven't been updated for new OS releases. If any Xtras with versions older than the current version attempted to load, a dialog would be displayed listing them, explaining that they might not work, and offering to check for updates (using webinstall, preferably), use anyway, or not load them.