If you are considering the XPS 15, you might also look at the E7470. I have been using one of these as my primary machine for several months now and have been quite impressed. The high-DPI display is fantastic, it's built like a tank, and I've had no compatibility issues whatsoever after a firmware upgrade. Moreover, it runs at a reasonable temperature and I can get 7 hours out of the battery if careful (`killall -STOP firefox` is a must, unfortunately).

The only minor annoyance was the lack of driver support for the Alps touchpad hardware. Thankfully, after poking and prodding enough people I was able to get specifications and implement driver support. I do wish that Dell, et al would be more proactive in pushing their vendors to merge driver support but oh well.

All-in-all, I'm very pleased with the machine.