And if you want a view into some of the current status of the ADS-B Exchange multilateration (MLAT) network, check out the sync stats page: http://www.adsbx.org/sync/

Select a region to see the details. For example, here are the feeder health stats for the southwestern U.S.: http://www.adsbx.org/sync/1B/

And here's the map of feeder locations in that region: http://www.adsbexchange.com/coverage-1B/