The Seagate Momentus XT 500GB hybrid hard drive (4GB SSD, 500GB HDD) is a useful way to speedup system boot and execution. However, on brand new files the speed is the same as a typical hard drive. A USB 3.0 drive adapter shows what the drive could do over a USB 3.0 link, using Disk Utility on Ubuntu.
Average read speed: 90MB/sec. Average write speed: 97MB/sec.