ManageWP is a WordPress service that allows you to manage all your WordPress sites from one, easy to use, dashboard. You can keep your WordPress sites updated, remotely manage all day-to-day tasks, perform automatic backups and more.
You can install themes and plugins in bulk across sites. You can do a full backup or database backup of any of your sites, and there are automated daily and weekly backups.
The “bulk add” features means you can publish new posts or pages and add bookmarks and users across some or all of your sites using ManageWP.
ManageWP is free in Beta status and the only limitation is maximum 100 blogs per account.
Info: http://managewp.com/
User guide: http://managewp.com/user-guide
API for developers at: ManageWP.com/API
ManageWP Worker plugin allows you to remotely manage your blogs from one dashboard.
Main features:
Secure! No passwords for sites required, uses OpenSSL encrypted protocol
One click upgrades of WordPress, plugin and themes across all your sites
One click to access administration dashboard for any site
Bulk publish posts to multiple sites at once
Bulk upload themes and plugins to multiple sites at once
Automatic backups of your sites
Clone one site to another
Download plugin: http://wordpress.org/extend/plugins/worker/