First, it was Tumblr’s “reblog this” feature on WP.com blogs. MovableType was the first to implement the same feature which The Blog Herald labeled as WordPress and MT being envious of Tumblr’s bells and wistles.
Allow denoting a post as a certain format. Some example formats are aside, gallery, link, quote. This will allow themes to style these posts according to format.
As of today, the only way to have this functionality in WordPress is by using third-party plugins. But it would certainly be a nice addition to WordPress’s native features. I wouldn’t call it ripping-off Tumblr nor another case of WP being envious of what the former already has.
It’s more of WordPress learning from what others are doing good and listening to what its community of users think would be a good feature to have in the blogging software.
I would personally love to see those features built into WordPress. Besides, it all started when the P2 theme was released. A WordPress blog was turned into a Tumblr-erized, so to speak, using that theme, but it was something purely cosmetic, because you loose those features once you switch themes.
So incorporating post formats into WP 3.1 is another step in the right direction. How it would affect Tumblr though remains to be seen. Though I’m guessing it wouldn’t make us dump our Tumblr blogs once WP 3.1 comes out.