@kurrik I'm having a similar issue with the "view media" preview in tweets... I use a wordpress.com blog and I cannot get the preview to show in tweets with a blog post shortlink. I have adjusted privacy/sharing settings in both wordpress and twitter, I've auto-published from the blog to twitter, I've posted both the full link and a shortlink... tried everything I can think of... and it still will not appear.
I've searched all over Twitter help forums, Wordpress help forums, google, etc., and I'm not fully convinced I need to apply for Twitter Cards, because it seems like wordpress & twitter allow the preview for others' blogs (http://bit.ly/Tb3hKU | http://bit.ly/RBlPCr | http://bit.ly/SeoXGM) but not for mine. Although the Twitter Cards seems like the closest answer. Here is what I see when I tweet a shortlink of a wordpress blog post: http://bit.ly/RdVXbi
If I need to apply for Twitter Cards to have a simple preview, please let me know. I'm not sure where I would embed code in my free wordpress blog, since I don't write the code for it, just the content.
Thanks for your help!