If you're like me and have been looking for a cost-effective way to "go diskless", you might have considered iSCSI. While a few offerings have appeared, these are quite expensive when compared to IDE/ATA/S-ATA (free), GbE-NIC (included free in many chipsets but no more than $50 as a stand-alone PCI card), and Parallel SCSI (again, no more than $50).
A GbE NIC seems like a great choice. PXEBoot can be used to at least run from a remote PXEServer (free with many Linux distributions), but often requires a non-free (for Windows anyway) PXEClient to do more than just boot diskless (i.e. to "run" from the remote disk as your C: drive).
iSCSI should inevitably be incorporated into the standard BIOS and driver set and get rid of the PXEClient issues. But then there is the performance impact of running the iSCSI and TCP layers entirely in S/W.
A few iSCSI possibilities exist, but a new entrant from Broadcom crushes the price model of those earlier entrants. The latest news of such a device can be viewed in Byte&Switch Article