From the first day they were anoounced, I was excited about the introduction of post formats to WordPress. It seemed like the next evolution of blogging to me, allowing users to go beyond regular posts and share videos, quotes, statuses, images and more.
It never seemed to catch on with everyone. Very few WordPress designs were created that supported post formats natively. Most of the themes that do support it are Tumblr style designs that were created for personal blogging. This was something that was about to change with the integration of a post formats user interface directly into the post editor. I am sure more theme developers will accommodate post formats once the user interface is introduced.
Mark Jaquith announced recently that the post formats user interface will not ship with WordPress 3.6. Instead, it is being taken out of the core and released as a plugin. He noted that he fought hard for it to be included in WordPress 3.6 but it just is not ready. The whole thing has delayed the release of 3.6.
What is interesting is that WordPress plan on re-introducing post formats to the core at a later date. I cannot think of any other feature that has been removed from the core with the promise of being added back later. I'm happy that it will be brought back as theme developers are not going to start supporting post formats until it is right there in the post editor for everyone to see.