Hello, compatibility! Microsoft's obviously a major proponent of Exchange ActiveSync (EAS), but if you've been using electronic mail for any length of time, you're probably aware that IMAP is a darn near universal protocol. Now, Microsoft is adding IMAP (and OAuth) support to Outlook.com. In addition to this being a lovely sign of Microsoft not shunning rival standards, it also opens up a ton of new possibilities. For one, applications that haven't supported EAS -- programs such as Mac Mail and the Mac edition of Mozilla Thunderbird -- can now host Outlook.com accounts.
Moreover, IMAP gives devs the ability to build third-party clients and services that are useful to end-users, and Microsoft's announcing the first set of those as well. TripIt, Sift, Slice, motley*bunch, Unroll.me, OtherInbox, and Context.IO have taken advantage of Outlook.com's new IMAP capability and are rolling out updates today that allow their apps and services to integrate with your Outlook.com email. If you'd like for your own app to follow suit, Microsoft's providing a bit of instruction right here.