The switch on a Cosmos S works just like a regular power switch, except the button is touch sensitive. It's similar to using the touch wheel on an ipod, in that it only reacts to contact with exposed skin (not through clothing, etc). If you hold your finger over it for several seconds you can reset your computer, just like most other single button power switches. Pretty simple, really. I could see how one might inadvertently reset their computer due to the nature of the design, but I've never had an issue with it.
I would say I prefer a touch sensitive switch to a standard button because it will likely never wear out due to the lack of moving parts. I've had cases where the power button has worn out and I've got to say that it's a real pain to deal with. Fiddling around with the button hoping for it to engage by pressing it just right, and then when you actually need to reset you comp you can't because the button is jammed. Like the other poster who owns the case mentioned, it wasn't the reason I decided to buy the case, but the touch sensitive button is certainly a plus in my book.