According to the site, "users may experience difficulties" browsing Xbox Live Indie Games, the Games Marketplace, or the Games for Windows Live Marketplace from either an Xbox or a PC. It's more than "difficult" -- in our case, at least, the XBLIG page returns no results at all.
Given recent history, it's tempting to jump immediately to topic of hacking. However, there's no evidence of that, so we're going to assume the blame lies with molemen instead. Molemen are stealing our Marketplace access.
Update: Microsoft sent Joystiq a statement attributing the outage to "an internal operational error," which it is working to resolve "as quickly as possible." You can find the full statement -- which does not confirm or deny the involvement of molemen -- after the break.