A qualified hit is an extra statistic for you to use as you see fit. For example if you had a multi-page tour and you wanted to see how many surfers got all the way to the last page you could put a qualified link at the second to last page to the last page. This would allow you to classify this as good traffic.
To setup qualified clicks, all you have to do is take the Qualified click link off the top of each Site edit page, stick it on the page replacing the link to the page you'd like set as qualified (second page if you'd like to set up second page unique
hits), and change the page.html at the end of the qualified link to the name of that page (page 2 on second page unique
hits).
You can track pre-join page hits as qualified hits and add them to your statistics page as such. Instead of using the qualified click link, you can cheat and add &qualify=1 to the end of the pre-join page link.