I guess that I shouldn't really call the Amazon discussions "forums" in the strict sense of the word. My guess is that you have already seen them and I confused the issue by using the word "forum" (though Amazon does also use the word "forum"). The whole Amazon setup is a bit different from forums like this one. Amazon titles them "Customer Discussions".
Anyway, the quickest way to get to them is to go to the Kindle store and scroll down to the very bottom of the long page. Just under the last Kindle Product Review, you will see two sections. The first section shows the most recent "Customer Discussions". The second box shows "Active discussions in related forums".