Is it usable? Yes. Assuming that you have a motherboard that supports it, all that will happen is that the data used most frequently after you install the SSD and enable Smart Response will be cached. This will mostly be your OS.
Smart Response is supported by a recent Intel chipset; if you have a board without this chipset, there is no Smart Response. What model of motherboard do you have?
Have you read the Tom's article on Smart Response benchmarking? If not, look it up under Articles, then Storage.