The Confederacy of Independent Systems had a base there, but were wiped out by Darth Vader. Vader then tried to choke his wife, and nearly died after a long duel with his former master, Obi-Wan Kenobi. Caused by a lapse in creativity in the Clone Wars writing department, Mustafar was also used by Cad Bane for something. Anakin Skywalker went there and found it to be a nice vacation spot. Despite this, the CIS was able to set up a secret base there later in the war. The Seperatist strategy during the Clone Wars was to simply return to planets conquered by the Republic. It is not known at this time who was to blame for the success of this strategy, as the Republic seems to lack belief in occupation forces. Because they were boring.
Some miners. And fleas.