They've said on the latest commentaries that 13 episode seasons were killing them, so they worked it into their deal with Adult Swim that they'd produce 10 half hours per season instead. There are only 8 episodes in the season proper, but the double length premiere and the Halloween special bring it up to 10 half…

I was a Nielson household three or four years back, and I was still sent a diary that had to be filled out by hand. My fiancee's family was sent a diary sometime last year, too. I think it only covered a week of viewing.