If your chipset supports it then Intel Turbo Memory can be used to speed up booting and speed up the load time of applications, it has been optimized for that purpose. Without it, loading youc Browser or Word on a morning can take a few seconds. With it, they will be more quick available than when they are on the disk and can take only a second or two.
A real life example follows...
My previous laptop had a Intel Core 2 Duo T7500 and 4 GB DD2-800 with the extra Intel Turbo Memory,
my new laptop has a Intel Core i7 720QM and 4 GB DDR3-1333 without an extra Intel Turbo Memory.
The hard drive is the same but on my new laptop applications tend to load a bit slower,
but well, one of these days I might consider to buy me a SSD which would speed up a lot of things.
Unless you have a Turbo Memory module I think it is better to get yourself an SSD than Turbo Memory.