I quite like this idea, as it's great to get other OS's on commercially available machines for people who want them, and the hardware on this is definitely upper echelon, but I question if this is the right price range to push with a free OS. Simply put, one of the biggest advantages of Linux is that you don't pay the licensing fee, so packaging it on a machine where only a small fraction of the cost is constituted that OS minimizes that advantage. Also, laptops costing $1500'ish are a bit of a niche or business item anyways, so market penetration isn't going to be spectacularly high. I'd rather see some $400'ish laptops with Ubuntu on it to actually push it. On top of that, most Linux enthusiasts are capable enough to get the machine they want and stick Linux on it, so they can pick and choose.
It may not be Dell's intention to pick Linux, and my guess is they have very low sales expectations for this item. In any case, good thing - I hope to see more machines, and lower end machines pre-loaded with various Linux builds.