Nielsen has a politics blog now:

The final night drew the largest audience so far for the Democrats (24.5% of all American homes), eclipsing the audience reach the three previous evenings.

Also, from TV Week, note the Lieberman review:

The second day of the Republican National Convention ended with NBC’s prime-time special winning a competition of small audiences.

According to preliminary national data from Nielsen Media Research, the three broadcast networks combined racked up a viewership of less than 11 million viewers, compared with the 14.8 million viewers who watched the networks’ coverage on the comparable night of the GOP gathering in 2004. That's also down from the 12.48 million who watched Senator Hillary Clinton’s call for unity among Democrats last week at that party's convention in Denver.

Two factors are worth noting: Hurricane Gustav's assault on Louisiana had essentially set back the Republicans’ attempts to get momentum by a day. Also, Democrat-turned-Independent Sen. Joe Lieberman’s speech, which closed the GOP show in St. Paul, Minn. Tuesday night, was not expected to be a stem-winder—and it lived up to expectations.