On 30th June 2011 Google Banned http://co.cc domain and it resulted all the subdomains got delisted from google search results. This was a very big loss for many bloggers who was depending on free domains from co.cc. All the hardwork done by the hardworking bloggers is lost now. This is one of the reason why you should not rely on free domain names and hostings.
As we all know that co.cc names were badly used for spamming purpose and they were unable to work on this regard hence google was left with no choice than to penalize this domain. Now the people who were using co.cc service are left with no other option that to move to either paid domains or some other free subdomain service. But the worst part is that the entire work done for backlinking and other off site SEO works is lost with this move of google banning .co.cc domain.
Those who are on blogspot originally can very well use the blogspot subdomain and continue the the blogging but i suggest you to get a nice domain for you. You can get a domain name just for a dollar from godaddy.