No, no. It’s not about having social bookmarking buttons on our Flickr photos. But, the idea is still about sharing. We are now able to share our photos, sets, collections with other members. And, it’s not only about sharing pictures with other members, but also related to how we will use the photos.
The “Share This” button will be visible only if we can share the information on the page. So, it is not visible on frontpage since we can not share anything. If we’re seeing a photo — our own photo or other member’s — we can easily tell other people about the photo, embed it into our websites/blogs, get the permalink, or even blog about it from our Flickr account (only if we have blogs assigned into our Flickr account).
Of course, we can not share our private pages like Flickr stats page (for Pro members). And, it depends on the privacy settings we apply to our photos. If we want to share some private photos, we can do it by giving a “Guest Pass” to our friends. Go to Flickr help page about sharing for more info.