I like the idea of post formats, because it somewhat meshes with my blogging pattern. While I also write longform posts, I also want to post just a link with commentary, or just an image, or just a gallery, or just a quote... The formats capability helps to "shape" the content appropriate to the selected format. Yes it's a little more work in the templates, but I think it adds some...appeal to posts if nicely implemented.

The obvious downside of course is that not all themes support them, or all of them, or consistently, even. I've been using the Crowd Favorite plugin (originally by Alex King) for some time because it adds in functionality that persists across themes. So that metadata can be theme-agnostic.