I got the fully maxed out one. 15.4" / 2.6GHz / 750m / 16GB RAM / 1TB SSD.
I will be using it for many different tasks, light stuff like Email, Web browsing, remote server administration, book reading, music listening & video watching.
But I'll also be using it for heavier tasks like Programming, Virtual Machines, Photoshop, Aperture and Final Cut Pro X.
So for me it's an everything machine I'll be doing almost everything you can imagine with the computer.
The main reason I went for the full spec is I will be using all this software ^ so I needed the power it provides, but also I will be keeping this computer for at-least 3 years minimum. I'm well aware (having been buying Apple laptops for over a decade) that the specs today quickly become obsolete and since we cannot upgrade the RAM and the SSD upgrade path looks uncertain I decided to max both of these at the point of purchase.
I will admit I don't need the 1TB SSD in storage terms, I mainly went with that as I know from buying many many SSD's that the higher the capacity the higher the performance and I was correct this time around as the 1TB SSD in these new models reaches almost 1GB/s read and 0.9GB/s write which is almost 100% utilisation of the 8Gb/s bandwidth provided by the PCIe connector the SSD sticks use. This extra boost is certainly nice not that the 512GB SSD isn't fast though.
TL;DR Need highest specs for apps and longevity over 3 year minimum ownership.