The old hybrid drives from Seagate and Samsung were doomed to failure for a number of reasons. First, they had just 256MB of MLC flash fronting a 5400RPM disk. MLC limited write performance, and since the small size made the Flash component smaller than the working set for an application like Photoshop or Final Cut, systems were going to the slow hard drive way too much. Finally, and most importantly, they relied on Windows Vista's ReadyBoost and other coding tricks to decide what data should go in the Flash.
Microsoft over emphasized boot-speed over improving application performance, so Windows DLLs were in Flash while application temp files spilled over to the slower disk. Add in that Vista was generally despised by the kinds of geeks that try hot new disk tech and then convince their friends, families and employers to use it and hybrid drives never took off.
Seagate's new Momentus XT addresses these problems and delivers a nice mix of speed, power consumption and capacity. The new drives have 4GB of SLC flash setup as a cache so no operating system support is needed. The Seagate folks say they specifically cache blocks that required head movement to access so the cache should speed up real world workloads by reducing the amount of head motion the drive has to do.
Seagate was kind enough to send me a pair of drives to play with, and like a kid on Hanukkah, the first thing I did was rip off the wrapping and stick one in my Macbook Pro. The Macbook badly needed a drive wipe and fresh installs of OS/X Parallels and Windows 7, so I took out the 497 little screws, changed the drive and put back 495. As usual, I had a few screws left over (or just loose), but the laptop felt way peppier than with the 5400RPM drive that was in there. In addition to speeding up my laptop, I wanted to run some real world benchmarks against the Momentus XT.