I remember buying a 80GB Intel SATA SSD (which was $450 USD at the time) and putting it into the DVD drive bay in a 2009 17" Macbook Pro. At the time there was no official SSD support, but there was an aluminum holder you could buy to remove the slimline slot loading DVD drive, and put a 2.5" form factor (7.5 or 9.5mm?) height SSD or HDD in its place. Was a huge performance increase for the OS/boot drive.