Now that the new generation of Windows Live web services has been released, Microsoft shared some facts,
"Like many sites, Spaces, too, struggles with the never-ending battle against spam. Improving in this area was a big priority for us, in both Spaces and Hotmail. Our efforts here're already showing signs of success. For e.g., during heaviest period of attacks on Spaces, a spam-tracking website called Uribl attributed 1500 spam campaigns to web pages hosted on Spaces, each of these actively generating hundreds of thousands of Spaces spam attacks. As of this writing, we've blocked 99% of these spam campaigns, so now Uribl lists only 15 active spam campaigns on Spaces, all of which're fresh attacks that we're actively working to disable. Very shortly, we'll put even more safeguards in place to ensure that fewer spam spaces get created, which'll bring this number down even more."
you can still allow public comments on your space, but by default it's limited to just "friends." But you can go to Profile page and click Privacy settings. Click Advanced, and then you can change permission slider for "Comments and notes" in the "Who can contact me" section near bottom:"