I just bought a new Samsung 120gb EVO SSD for my LR5 cache/catalogue folder (55gb). The drive was $89 at Tiger Direct.
Huge, amazing, earth-shattering difference in Library mode. There is now no wait at all for a folder with 1,000 images. They are just there, ready to be clicked/developed.
I've had the actual Lightroom program on my Intel 120 GB SSD for years, which was a big boost as well. My actual RAW files are on the platter drives.
Definitely recommended.

