For the full story: [Official Thread] Welcome back HTML Embeds! Goodbye to some sharing options.
The salient part is:
Secondly, we are announcing that we are deprecating the support for our built-in sharing options for WordPress [Ed: spelled in the original with a small "p"], Blogger and LiveJournal on 3/25. Deprecating features is never an easy decision, but we have seen that all of these services combined are now adding up to less than one percent of daily share volume from Flickr.
Which I understand to mean that this method will no longer be supported: http://en.support.wordpress.com/images/flickr-photos/#blogging-your-photos (link to Internet Archive)
Meantime, the flickr HTML embed option is being brought to the “new flickr experience” in addition to the current iframe embed, which we cannot use here on WordPress.com.
Of course, this does not affect the WP o-embed method of copying and pasting the link of the flickr image page on its own line in your post or page. Or at least I hope not!