Considering the cost these days of securing a domain, it really wasn't that big a deal, but it did make it easier and more inviting to test out the product. In many cases, as the web designer portion improved, many landed their primary websites there.
In the event you didn't get the memo, the renewals aren't free anymore.
Beginning October 1, those who 'accepted' a free domain for Microsoft's Office Live (most were registered through Melbourne IT with a One Microsoft Way admin address) will be charged a $14.95 (US) renewal fee as they begin to expire.
I'm sure there are many who don't check their associated e-mails anymore (or often) so this is simply a heads up that if you did register a domain name through Microsoft that you absolutely LOVE, you may want to head on over to this page to check out the upcoming changes.