The chart below displays the number of scenes visible to all users on EarthExplorer as of January 31, 2016.
In addition to the current Landsat 8 and Landsat 7 missions that are constantly increasing the data in the USGS archive, the Landsat Global Archive Consolidation (LGAC) effort is returning unique Landsat 1-5 MSS and TM data originally downlinked to International Ground Stations into the USGS archive, making even more data available to all users.
The files on the USGS Landsat Global Archive webpage provide a view of the data added to the USGS archive per satellite, per year.
The image below shows the Iguazu River area in Southern Brazil, in one of the most downloaded scenes from the USGS archives in January 2016.
Landsat 8 Path 222 Row 78
Acquired January 18, 2016
The Landsat archive became available to all users at no charge in December of 2008. As of January 31, 2016, over 34 million scenes have been downloaded by users worldwide.
This graph shows the top ten Landsat data uses from October 1, 2015 through January 31, 2016.