If you're using the standard zwiki skin insite a plone site, the subscribeform doesn't show the subscribe buttons. You have to switch back to plone skin.
clarification --simon, Wed, 08 Feb 2006 18:38:47 -0800 reply
The standard skin's subscribeform inside a plone site shows buttons based only on the user options email cookie, it should also check the authenticated username like the plone skin's subscribeform. Something like that.