Jon Udell takes a look at collaboration in Microsoft's Office 'system':

Here’s a trick question: What is Microsoft’s collaboration server? The answer used to be obvious: Exchange. Now it’s not so clear. Suppose you want to hold a discussion. You can still do that transiently in an e-mail thread, or with more permanence in an Exchange public folder. But Live Communications Server injects a new ingredient into the mix: IM-style presence. If you can see that the participants in the thread are online, you may want to switch to chat mode. Or you could launch a discussion on a SharePoint site that displays presence indicators. Even more intriguing, an Office document can now be a locus of presence-enhanced SharePoint collaboration.
...Users will find no single unifying theme akin to the Groove shared space.