Apparently a "good portion" of people attempting to visit the site were instead going to O.com, a single-letter domain still reserved by ICANN.
The company plans to return to its former Overstock.com branding on its Web site and in TV and online ads for the holiday shopping season. But the company will stick with the O.co for international and mobile efforts, and the O.co sign will remain on the Oakland Alameda County Coliseum throughout its six-year naming contract.
I think that Rick Schwartz had a number of blog posts about o.co and how the investment value of domains in .co ccTLD had changed. In some respects, he is right. The .co ccTLD is in its First Anniversary drop at the moment and many of the junk domains will drop during this period. However now is the period when much of the insane early market valuations for domains in a new TLD change.