Today SanDisk revealed Vaulter, a 8GB or 16GB flash drive that can hold your entire OS, designed to sit on the PCIe port inside a laptop. In Windows, this creates a separate letter drive, which speeds the hell out of your computer, without taking the place of your 2.5" SATA-connected HDD. It's not a Santa Rosa "Robson" thing either—it's a real drive, not some caching assistant. (In case you're wondering, Mac support is coming.) Performance acceleration comes from "pre-controlling the distribution of storage data between itself and the hard drive." The fact that it's on the PCIe port means that both storage devices can work in parallel. Now, the bad news: SanDisk is only offering it to OEM partners at first. We won't be able to buy them a la carte for a little while. [SanDisk]
There are already solid-state expresscard drives this size that are ridiculously overpriced. You could just upgrade to a solid-state drive in a new laptop at that price range. And as many stated before, you would need an available internal PCIe port, which many older lappies don't have.
This is another great concept that is couple years too late.