Five Powers (plus my Terran White Fleet as a rebel faction), I ended up using just the Aquarian, Avarian, Carnivoran, and Entomalian forces and left the two Terran fleets in the box (sorry, Scott!). You'll notice I also had calculators for everyone, as there's some (simple) math involved in Starfleet Wars.
Hill Cantons played the Avarians; Chip "da Baron" directed the Carnivorans; Joe, our host for the Johnny Reb games I've blogged about, took the Entomalians; and I had the Aquarians. The objective of the game was to gain control of a mysterious alien artifact of the ancient Mag'Uph'Un Empire that all four competing fleets had coincidentally encountered at exactly the same time.
None of the other participants had ever played Starfleet Wars, and while they missed the vector movement of Galactic Knights, they all enjoyed the simplicity of SfW, which still required difficult resource management decisions. And even though tracking power usage meant sometimes consulting the calculators, we still got through a 12-turn, four-player game in about three hours. I will definitely be playing this game again, and maybe running it at the next con I attend.