For me, it is one of those 'little touches' that adds to the bling/wow factor. It actually IS useful in darkened environments even though I can touch type.
The first time I had my new MBP at work (I have the only Apple computer there), we were in a conference room, they hit the lights off, my display auto dimmed and the keyboard lights slowly faded up and several people freaked out. They thought it was the coolest thing! *NOW* they want Macs.
Of all the stupid reasons to finally want to switch, this is what did it for them. One picked up a new Macbook, and the other got an iPhone and is saving for a Mac. The third had already had his iMac on order.
The other three people said 'Macs are stupid!'
It's crazy.