I had to turn comments off on most of my blogs due to a large scale comment spam attack from China. If you check the IP addresses for spam comments, about 95% are coming from China, regardless of the comments posted. The IP addresses are not visible in WordPress, but they are in the database and can easily be queried in phpMyAdmin.
One of my blogs still has comments enabled, but I have the comments set to automatically close after 90 days. It appears that the automated spam comment bots target older URLs.
If you run multiple blogs and use Akismet, Akismet will shut down your account during an attack. They only allow a limited number of spam verifications per hour. I was getting over 250 spam comment submissions per hour on each of several sites during the attack.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin