With Surface 2's and Win 8.1 RT release, more users will be getting a look at the Outlook 2013 version included in Windows RT. While all of the basic features are available: you can connect to multiple Exchange servers, EAS, POP3, or IMAP accounts, send email, use the calendar and contacts, you can't use macros or install add-ins. The add-ins that ship with Outlook work - you can sign into the Social connector, but can't install 3rd party add-ins.
Junk mail filtering in Outlook is disabled for POP3, IMAP, and Outlook.com accounts. It is working for Exchange server mailboxes.
Custom forms may or may not work. Simple forms are fine but some custom forms containing controls won't work. You can design and publish simple custom forms. (If the Publish button is missing, restart Outlook.)
Managed mailboxes and public folders sync, but Online Archives and Archive Mailboxes are missing. Other corporate features such as group policy, applying retention policies or IRM are not supported. The Infobar doesn't display information about polices that are applied automatically, however, Mail Tips work, as do Outlook Apps (if you use Exchange 2013).
Internet calendars are supported but you can't connect Outlook to SharePoint lists. Naturally, BCM doesn't work. The Lync app isn’t integrated with Outlook.
Bottom line: the typical Outlook user won't notice any differences. Power users won't have all the features they are used to, but it's more than serviceable. It's as quick to use as a smartphone, but with more features and a larger screen. Great battery life too.
Outlook 2013 RT appears stable, however I've noticed that the Reply and Forward buttons sometimes disappear until Outlook is restarted.
Below is a screenshot of the People Hub in Outlook 2013 RT. All of the features found in Outlook 2013 are available in the People Hub, except Lync presence in the contact photo.