Some file sharing schemes did work this way, but they were primarily used for sharing video editing files. Most fibre channel SCSI works this way.

On Macs, though, you need a SCSI card which will let you change the SCSI ID of the controller itself in at least one of the machines, then you need software which "locks" the drive for all but one of the machines (or you can write everything to the drive with one system, make it read-only, then let both read it). Transoft was one suite of software which did this, as did Avid's old file sharing (I don't remember the name of their stuff right now).

It has it's place, but it's a very limited place.