Drupal Gardens is a gem in the rough, built on the Drupal 7 core - currently in an alpha release - extended with functionality such as a WYSIWYG editor (CKeditor), media management, a theme builder, and basic "query builder" (i.e. simpleviews) capability. We're working with the various module maintainers, and contributing back almost all of our development efforts to the Drupal community. Architecturally, Drupal Gardens is built on the ideas of an open social web; we markup data with RDFa, we implemented single-sign on using OpenID as our identity layer, we integrate with third-party services, and we allow people to export the code, the theme and data that makes up their site. We'll be sharing more technical details as we make progress, but we like to believe it will be a hosted service "done right".
Check the video on the Drupalgardens.com homepage. There's an other one here: http://www.cmswire.com/cms/web-cms/drupal-goes-hosted-launches-gardens-in-private-beta-006537.php