The MHz difference truly is irrelevant.
MacWorld's benchmarks show that the 2.4GHz model is this much faster:
18 seconds for a ~2 minute Compressor encode
6 seconds for a ~1 minute iMovie HD effect
3 seconds performing a ~1 minute Photoshop macro
Can anyone possibly say that this sort of performance increase is actually worth £200?
Well, I understand your viewpoint perfectly; however, I have a quite different case than many people here.
My current computer is an HP dv1660se which has a 1.66GHz Core Duo. The keys on the thing are black and the LCD is not that bright without having to distort the coloring of the screen. So I am a person who is going from Winhell to Mac OS X and person who would like to see more processing power [I find a 8.GHz difference alot of change from where I'm comming, specially now with Snow Leopard nearing every day].
Also, I have experimented typing with my black keys at night, at the airport, in the plane and even at dawn/dusk. It is hell having to position the LCD in a way that allows me to see the keys but not see well the screen itself, so yeah, Backlit is a nice thing to have now.
Hard drive wise, my current Hard Drive is 80GB (as advertised in that time), the actual thing is only 72GB with the disk being partitioned from factory into the main partition for Windows being 64GB and the other partition for "recovery reasons". Currently my disk is full and have only 1GB free [just about free enough to manage my day to day computing]. So yeah, 250GB is welcomed by me with open arms.
Now price wise. My current HP costed me $1200 when I bought it [it had the Vista Capable sticker which made it more expensive (although I bought the machine since it was on sale, not because of the sticker), now I'm crossing my fingers that the lawsuit against M$ hold and I get a nice check from them or HP]. So going from $1200 to $1500 is not much of a difference. I say $1500 since I can use my student discount

.
Now, upgrades, my parents are not paying for my new Mac, I am; however, the upgrades are going to be a gift from my parents as a happy 21st birthday for me, so 320GB and 4GB Ram for the win!! (I'm buying the Mac on my birthday btw)
So, yeah, I'm pretty excited and having saved alot of $$ from work sure does pay off now...
Well so that's my story for wanting the 2.4GHz model... what's yours??