The easiest, fastest, most light-weight WordPress Cache plugin available.
Once you have turned 'On' Frontend Caching from the WP-Cache.com menu within your wp-admin, you simple can log out of WordPress and head on over to your frontend. Once there, just refresh the page, then look at the source code of your homepage. You will see at the very end of the source code just below the closing tag a comment indicating that WP-Cache.com generated the page from cache.
No. WP-Cache.com does not cache the wp-admin backend. In fact, WP-Cache.com doesnt even serve cached files to the admin.