I saw a plugin called "Press This Reloaded" which adds a bit more of the normal WP post options, yet no auto summary and featured image of the URL/article being shared. Alas, I will play with the normal Press This some more to see if I can add featured images the way you're describing.
My Twitter & Facebook are full of cool articles I share, and I can even add a little intro about the article I'm sharing (in addition to the article title, summary, and thumbnail). So was looking for a way to share in this manner to my own WP blog.
I actually saw a preview/demo of a new template being released by Michael Hyatt (www.michaelhyatt.com) that includes what I'm describing as a "Post Type." I wish more templates were created like this, or maybe there's a plug-in that would do this for me? His Post Types allow him to post articles, announcements, events, and URLs. Also books. If he does a book review, the title of the post links directly to the Amazon page. Check out his blog and post types. Pretty groovy. http://michaelhyatt.com/get-noticed-wordpress-theme.html
Another template I found that is built for nothing but sharing URLs is http://www.premiumpress.com/demo/?t=directorypress. It shares a thumbnail of the website, which becomes the featured image, but auto generates a title and short summary. This will work for any sites I build dedicated to sharing URLs of specific categories. But for my existing blog, I sometimes really do blog, LOL, so this template is not a match for my primary blog.
Anyhow, I'm probably rambling at this point. Thanks so much for engaging me and at minimum re-pointing me to Press This. I can certainly use this is an interim solution with my beloved Google Chrome browser :)