What are the pros and cons of SSD caching

Is it worth doing? As I understand it, you can add a relatively small SSD to a rig that's running on a regular HDD, and then using, for example, Intel's Intel Rapid Storage Technology, implement caching and it will improve the likes of boot up speeds, as well as enhancing the performance of commonly used programmes.

What are peoples' experiences with this? Does it provide equal or better (or worse) performance then having your OS and programmes on an SSD and data on an HDD?
 
I think it's better just to have an SSD if you want better performance. SSD's grew faster themselves in capacity and speed while slowly dropping in price. I think SSD caching was implemented a little late or SSD's just advanced too quickly.
 
I have the SSD as my boot and steam running on it, and it is lightning fast. even my relatively slow ssd at 200MB reads and writes boots in less than 30 sec. and i am online at 45 seconds from power on. i have to login to my computer. even after clearing space on my laptop running an HDD to less than 10% filled and almost no startup programs (less than my desktop) it still takes 3-5 min to startup. so yes an SSD as a boot with OS is very beneficial and in my mind, very worth the money