I think it would be more descriptive for us newbies if the previews for WordPress themes actually showed an existing blog in that particular theme. I say this as I am having a little trouble picking a theme based on my content and a visual is my easiest way of learning. As it is I have the mandatory simple blah blah of WordPress that has not been replaced as of yet and which does not give an view of an aged blog with content and (especially) responses.
On another note, the process for a free blog locked my machine up repeatedly. Your front end definitely needs some revisions.
You can use the wp.com theme showcase site: http://theme.wordpress.com/themes/
After you click on a theme, you can see a demo blog if you click “See it in Action”, and for many themes there are links to actual blogs under “Who’s Using This Theme?”.