Anker appears to have an
inexpensive gigabit USB adapter. I'm not happy about not having it built in, but I won't have much of a choice when it comes to ultrabooks (plus I REALLY like that screen on the XPS).
When switching from a laptop to a desktop, a docking station of some kind is going to make your life happier. Docking stations will contain the gigabit ethernet adapter so you don't need to buy it separately. If you're lucky, your laptop manufacturer makes an actual dock, and if not, you can get a USB3 dock like
the one I got. I'm pretty happy with it.