Unfortunately, at this point in time, I cannot first difference the attendance data for the current NBA season, since the next NBA season (2012-2013) has not been played yet. Thus intervention analysis is not currently possible to analyze the impact of the NBA lockout.
So, using total league attendance does not help, since the number of games played is different, and it is too soon to use intervention analysis. Is there any alternative way to figure this out? Yes. One is to perform a t-test on the means of attendance. So, I downloaded the team-by-team attendance data from ESPN, and entered and sorted the data into Microsoft Excel, and then calculated a t-test on home team average attendance for the 2011-2012 and 2010-2011 NBA teams. The result of the t-test was that team-by-team average home attendance was not significantly different over the two seasons. In other words, statistically speaking there was not a great enough difference in the two data series to say that one is different from the other; and thus I would conclude that the NBA lockout did not have a statistically significant impact on average NBA team home attendance between those two seasons.
Alternatively, one could just plot the data over the last few seasons and look to see if there is any visual difference. While this is not all that technical, it does give some additional evidence that fans did not respond much because of the NBA lockout. Here is a line graph of average NBA home attendance over the last four NBA seasons. The line in blue is the 2011-2012 lockout season.
Average NBA Team Home Attendance: 2008/09 to 2011/12