co.cc isnt technically "free". You'll notice that there are tons of premium domain names (one word's, LLL's, etc) available, but they all have price tags depending on how valuable they are. The only way you can get a free co.cc is basically if you "invent" a word that the system determines to have no value. Just look at how "porn.co.cc" is still available, but it costs like $600/yr to register.
I am thinking about using one for just a personal site / blog but I don't know haha it just seems iffy as nothing is free...
co.cc is not bad. im using also co.cc just take a look at my site http://www.animejutsu.co.cc. I would suggest try to make your layout good and cool so that visitors will come back to your site and also make proper seo. mine is not yet ranked coz it's still new