Currently, even if a user add __NOINDEX__ to its talkpage, all threads created on it are *still indexed* by search engines, since the extension creates each commont in a different page (where the user can only add the magic word *after* the topic was created). The same happens for other pages (not only user talk pages).
For privacy reasons, this shouldn't happen. Specifically, the users should *not* be requested to add __NOINDEX__ to zillions of comments in order to get all of them not being indexed.
See also: