This isn't currently possible. The best you can do is subscribe to a tag to receive the questions via email or subscribe to the email newsletter.
If you think about how the system works doing AU via email wouldn't work, the entire point of the system is to not do post-reply-over-and-over, questions and answers are just edited as information about the problem is discovered.
As far as tags go, they should be used to describe the question you're asking. By default it seems that google at least picks up the first tag and displays it in the search results.
