AnandTech has a nice review of Gigabyte's i-RAM product. It's a card that plugs into a PCI slot that has 4 DIMM slots in it. You buy the card for $150 and then have to buy up to 4 RAM modules to populate it with. So, for about $500, you can buy yourself a 4GB solid state storage device that could be used for a number of things including your operating system's paging file, your boot device, your favorite game's storage area, or a number of other things where the increased I/O performance would give you the greatest benefit.
Hell, with Windows installed on your i-RAM device, you could boot up in 9 seconds!