The domain name Office.com could be attached to many things. It could be for an office supply store like Staples, or for NBC's comedy show, or even an application suite for productivity software.
Microsoft, however, has taken an extreme liking to the domain and recently purchased it from its previous owner for an undisclosed amount. Obviously, Microsoft intends to use the site for promotion of its Office suite of software.
Today Microsoft has officially taken over the domain and is pointing it to its website for Office 2007 products. Many believed that Microsoft was reserving the domain for its upcoming online productivity application services that would compete with Google Apps.
Microsoft could still use the domain specifically for its up-and-coming online services, but we'll likely have to wait until the launch of Office 2010 for that.
Just for fun, check out this Office 2010 promotional trailer that Microsoft commissioned. It doesn't offer much information about software, but it's entertaining for anyone who has spent time working on TPS reports.