In Outlook.com, the storage is "virtually" unlimited, to use Microsoft's words. (The company won't fully promise unlimited storage, since it needs a way to hedge against spammers.) That compares with 10GB of free storage on Gmail. Not bad, eh? Also, as you might know, every Microsoft account comes with 7GB of SkyDrive storage, so that's what you'll get if you're new to the company fold. Also, anyone can sign up; you don't need an invitation, and there's no limit to the number of people allowed to test the service in its preview stage.
Source: HardOCP | Outlook