For those wondering why a non-Apple user would want an iCloud account:
- To access Calendar services. Calendar on iCloud is available as a iCal service and a web service, allowing for many devices to access your calendar.*
- Mail is a standard IMAP based service and also accessible via a web interface.
- Reminders are standard iCal services and accessible via the web.
- Contacts are accessible via CardDav and web.
- Outlook no longer connects to Google as Google has deprecated their old connector. iCloud Control Panel is the only free method for integrating Outlook** directly with the push-enabled iCal, Mail, Tasks, and Contacts.
- Photos can be shared from the iCloud Pictures folder synchronized via iCloud Control Panel.
- Bookmarks can be shared between Firefox, IE, and Chrome.
- And to top it off, this is the only way non-Apple users can access the iWork suite.
All of the above services, including the web-based services, come with no ads cluttering up the user interface or reading your emails to create a master profile of your reading and thought habits to sell to third party vendors.
Why would a non-Apple user not want to use iCloud?
* Google egregiously restricts access to iCloud Calendar services, claiming that they can't crawl the service due to Apple's robots.txt. This is a lie (an iCal client is not a robot and does not "crawl" an iCal server and should never even request the robots.txt file), and is yet another way that Google tries to force you into their ecosystem by not allowing connections to other standards based services (e.g., Outlook connector killed, IMAP standard bastardized, iCal marginalized). This is relatively easily circumvented by using an iCal proxy; search for yourselves, as many are doing it with a few lines of PHP or Perl.
** Microsoft engineering has repeatedly integrated iCal support into Outlook during the beta phase of their development. When it comes time to go RTM on the product, management has repeatedly made engineering pull out the iCal support, so that Outlook will only fully integrate with Exchange servers. This has happened with every release since Office 2003, at least that I am personally aware of.