I wonder how much sense this drive makes - 4GB is a very very very small cache for a 500gig drive.
If the caching algorithm is very very very well done, it would be useful for caching OS and program files, and speeding up launches. Ideally, what you want cached is relatively small bursts of reads with non-linear LBAs... it the algorithm doesn't do something to avoid caching long linear reads, the cache will be evicted too easily, and you end up with poor performance.
The idea is interesting, but if it were to be
really nice, there should be a way to say "hey, I really want
this stuff pinned to flash" - either by über-fancy OS cooperation, or simply by the drive representing itself as two physical drives, one for SSD and one of HDD (wouldn't work well with Windows and a 4GB SSD, though).
Also, being read-only the benefit you get from it is going to be limited. There's still a lot of small-file scattered writes going on in today's systems.
Aha,
Jeff Atwood has a post about it too... he uses the term "near-SSD performance", though, which you should take with a couple thousand grains of salt
