After reading this thread, I decided that I would always be jealous of those with the lit up keyboard, so I decided it was worth the extra £170 to get it. I also wanted a bigger hard-drive, so this thread gave me the push I wanted/needed.
So the lit up keyboard is cool, however I was watching a movie last night in bed and turned off the lights on the keyboard so as not to distract from the screen, so then when I wanted to pause it or anything, I then had to search in the dark for the light button so that I could see the pause button! Essentially I could just have looked for the pause button, but I wanted to use my new lights! so in that situation, it really was a useless application.
However when the evening reaches that stage where it is not yet dark enough to turn on lights, the keyboard is very handy... or if you were to travel on buses evening times...
Otherwise I would say that it is a cool factor that may wear off after first two weeks, so is it really worth spending an extra 200 for two weeks of novelty?
I would say only go for the 2.4 only if you have other reasons such as speed, harddrive etc. and if you are not always in good lighting conditions. Also I tend not to look at keyboard while typing, and found it to be quite a distraction making me nearly second guess myself!