I've notice a good performance boost running my OS and programs from a solid state drive, while my data resides on a hard disk drive. My reason for keeping my data on a hard disk drive is that it is much more reliable than a solid state drive (I'm speaking from empirical experience). I've had the solid state drive glitch a couple times over the last year requiring OS re-installation. I was surprised that there didn't seem to be much difference between having everything on the solid state drive and having your OS and programs on the solid state drive with your data on a hard disk drive.