The i7 is the newer high end mobile processor from Intel. Are you going to be gaming with this or just want a higher end PC?
I'm on the fence. I'm looking at an Asus i7 model. A core 2 quad model is only a few hundred bucks cheaper but ships with Vista. By the time I do a Win7 upgrade, I might as well have gone with the i7. I believe I've ruled out the Core 2 duos for longevity reasons.
The only potential problem I see with the Asus i7 model is heat. A few reviewers mentioned that the laptop gets very hot when gaming. Since I'm not a gamer, I'm thinking I won't run into those GPU/CPU heat issues, but who knows. I always try to buy high end for longevity but if the i7 Asus laptops suffer from heat issues, they may not have too long of a lifespan.