Search "post formats" for 210 themes, on the official WordPress site.

Sarah pointed out:With all the discussion lately about why more people don’t make use of post formats, it’s refreshing to see themes showcase this feature in a beautiful way.

I was quizzical about that earlier post Sarah mentions, when it first came out. It said:

No, Post Formats haven’t gone anywhere but theme support and their use appear to be waning.
Several months ago, I decided to lay in a small stack of themes on my test-site, especially selected to educate myself about "post formats", the difference with custom formats, and related topics. I had no problem 'swamping' myself with a widely-diversified inventory of themes promising to showcase different ways to approach & utilize the post format feature. In fact, I had to 'discipline' myself, not to go full-on 'kid in a candy store'.

So I returned just now to the WordPress.org Themes download page, and performed the search linked at the top of this comment. There are 26 pages of search-results, each with 8 themes matching the search-criteria, and 1 additional page with 2 more. Glancing through the pages and making note of the submission-dates for these themes, they are generally quite recent.

I tallied the year-dates for these 210 "post formats" enabled themes:

2008 - 1
2009 - 11
2010 - 11
2011 - 20
2012 - 61
2013 - 90
2014 - 16

Regrettably, I did not keep an eye on the 2014 month-day dates, since if they were all in January, that means we are tracking on 192 new Post Formats themes, for this coming year.

That late-breaking trend-indication could be further-checked, by looking at the month-tallies for the end of 2013.

In round numbers, it looks we're probably in the midst of an explosion of Post Formats-supporting theme-development.

Now ... if I can only figure out what post formats are! ;)