Nielsen just released last night’s ratings of Barak Obama’s national campaign spot for the 56 local markets where we have meters.

Overall, for the six networks that aired the program simultaneously, the spot had a household rating of 21.7% (meaning that 21.7 percent of all households watching television were tuned to the spot.)
In comparison, the final debate between the two presidential candidates received a 38.3 household rating in the top 56 local TV markets. The candidates’ first debate on September 26 received a 34.7 household rating in the top 55 markets; their second debate, on October 7, received a 42.0 household rating in those markets.

The last presidential candidate to air a paid simulcast was Ross Perot in 1996, which received a national household rating of 16.8.
Last night, the Baltimore market had the largest TV audience, with a household rating of 31.3, while the Portland market had the lowest household rating: 14.2.

From the Nielson blog