In your faq you state:
How do I add my favorite WordPress plug in (plugin) or theme?
Currently no additions can be made to your blog as FTP access is not allowed. Suggestions can be made though via the Feedback form within your own Dashboard. (They make that suggestion here) New themes are usally added on Fridays.
This sounds like more than one theme is possible with WordPress.com. Yet in struggling to find anything in this site, I have yet to locate any real discussion (or index) of the choice of themes available, where they are added "every Friday," and how to apply a particular theme to my blog.
Most of the FAQ accesses the wiki that applies to WordPress.org. I already *have* a WordPress.org blog, Give Me Some Latitude, and have done some theme tweaking, though now all that shows is a change of color, in kubrick.
I moved to WordPress.com so that upgrades to the WordPress software would be transparent. It seems there is so much transparency here that I cannot even see actual themes!