Yeah... RAM disks are awesome!
I've got my OS on a ram disk... Unfortunately its bottlenecked by the SATA bus... They really need to start producing motherboards with a few DIMM slots for RAM disk, and the usual 4/6 for RAM...
My RAM disk is a PCIe board with 4 DIMMs on it, its got 8gb of RAM in it.. Its then got a lead that goes from the PCIe card to the SATA controller on the motherboard... The SATA bus is still a fair bit slower than the DDR2 modules, and therfore, bottlenecks the RAM disks potential performance. however it still destroyes the performance I achieved with 2x73gb SCSI HDD's in RAID 0...