Flashcache is the easiest to setup of the different caching layers available for Linux (bcache, dm-cache) because it doesn’t require patching the kernel and can compile as a module; better it comes with dkms support and builds smoothly on Ubuntu 12.10.
I’ve replaced my Lenovo cdrom with this Ultrabay http://www.amazon.com/gp/product/B008MH9DFG/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1 filled with a reasonably priced 64 GB solid-state disk.
I also setup laptop-mode-tools to be able to spin down the hard disk when on battery and it isn’t being accessed (like when all of the reads are cached). I’m happy to say that I’m getting 91% read cache hits today.
This cable http://www.amazon.com/gp/product/B005AKUS66/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1 was not easy to find, but it will let me use the old cdrom externally, and with other systems.