One way to upload a file for sharing is to choose Save to SkyDrive from a program's Share command. That brings up a dialog box for entering your Windows Live password to log into your SkyDrive and save the document to it. You can also use Microsoft Document Connection, a utility included with Office 2011, to upload files.
Once your file is uploaded, you can choose Share E-mail (as a link) from the program in question to send colleagues an e-mail with a link to your SkyDrive. In several attempts to share to different addresses this way, however, the e-mails never arrived.
Instead, I went to the SkyDrive with Document Connection, copied the direct link and e-mailed that. These e-mails did arrive, and once the recipients established their Windows Live bona fides, they were able to access the document.
Colleagues with Mac Office 2011 or Windows Office 2010 should then be able to work on the document at the same time as you. Office locks the program at the paragraph level, so your changes don't collide with each other.
Colleagues without access to the latest versions of Office can also work on documents in the cloud with Microsoft's Office Web Apps. But when I tried them, I found that the Web Apps didn't operate as smoothly as Google Docs or Zoho for online editing, but it preserves the original formatting and styles better than the other two online apps.
All in all, I feel about the Internet features of Office 2011 the same way I feel about Outlook: At least it's there for those who need to collaborate in a SharePoint environment or who don't trust the public cloud. But with Google Docs and Zoho so well established, and given the popularity of services like Dropbox for sharing files, I'm not sure what the compelling value would be in choosing the Windows Live plus Web Apps solution.
There are two ways to look at the value of Microsoft Office for Mac 2011. One is from the point of view of Mac users in a Windows-dominated enterprise environment who need all the compatibility and as many sharing features as they can get to work successfully with their colleagues. For them, upgrading to the current version will make a big difference.