According to Wired

• You cannot unsubscribe from the RSS feed's page at the Kindle Store, at which it says you are "already subscribed" but offers no unsubscribe option.

• You cannot unsubscribe from the Kindle's "content manager," which lets you delete other content. You may remove the actual downloaded data, but not cancel the sub itself.

• Nor can you unsubscribe while the feed itself is being displayed.