And have you ever used Momentus XT?
I have a 256gb SSD on my desktop as my main and 2xIntel 160gb as my application, plus terabytes of regular HDD for data. That's the basis for my comparison for the Momentus XT that's sitting in my x200s laptop.
If you go by benchmark, sure SSD is going to have the advantage in sustained transfer rate, but most people buy SSD for the response or the feel of responsiveness. People buy SSD because application launch faster. That's where the XT's NAND comes in. My x200s Windows launch faster, application launch faster, general responsiveness feels better. Before changing the HDD, my x200s is unbearably slower than my desktop, but after the swap, it is close to the experience on my desktop in day to day computing task.
Coincidentally, Anand just did a review on the 2nd generation XT, and from that and many other reviews, you will see the same experience. And that's from people with both SSD and XT experience.