I do, and I run one in addition to the dry-sump. They serve two functions:
1) as a safety to supply oil in the event that the oil pressure supplied to the galleys drops below a certain point (5 psi, generally)
2) as a prelube device-- pressurized oil can be supplied to the bearings before start-up
I put mine in pre- dry-sump, but am only using it for pre-lube now, as there's really no chance of exposing the oil pick-up to air or foam any more.
The principle is exactly like that of a diaphram pressure vessel for a well pump. The Accusump is a vessel with an oil chamber and an air chamber. There is a piston with a seal dividing the two sides. When oil pressure exceeds the pressure on the air side, the vessel begins to fill with oil. As the vessel fills, it pushes the piston into the air side, thereby increasing the air pressure. When the two pressures find equilibrium, oil stops flowing. If the oil pressure in a galley drops below this pressure, oil starts to flow back to the engine. This can all be controlled even more precisely with a solenoid valve arrangement and pressure switch. It's really the cat's meow.
I can't for the life of me figure out why more guys don't run them.