Google Maps told me that it would be about 38 hours of solid driving from my dad's place in Simi Valley, CA to my girlfriend's apartment in Raleigh—most of it occupied by I-40. The states traversed, either in part or in full, would be California, Arizona, New Mexico, Texas, Oklahoma, Arkansas, Tennessee, and a good chunk of North Carolina. I had allotted three days for the trip, and I needed to make the drive by myself in my BRZ.
I thought it would be a piece of cake. I was pretty badly wrong about that.
Okay, let's get this out of the way first.
States on I-40, Ranked
In the words of the not-at-all-biased band Best Coast, "Why would you live anywhere else?" On a side note, San Bernardino County is bigger than it looks on any map. You're blasting along through miles and miles of desert for hours on end, and you start thinking to yourself, "Did Arizona forget to put up a sign welcoming me to their state?" But no, it's just that the Mojave Desert (in Eastern California, that is) is a vast and mostly-uninhabited hellscape.
2. North Carolina
North Carolina is a very nice state. It might even be the best state in "the South," though as the consummate non-Southerner (being from Colorado puts you, somehow, in very shaky territory vis-a-vis being a "yankee") I don't understand this place yet. But there are lots of nice restaurants and people seem very friendly; also the roads seem fairly well-maintained, and a lot of people seem to have VERY nice rides.
This state is gorgeous (and, as a bonus, their roads are lovely and smooth!). Truthfully, my journey through Arizona coincided perfectly with late afternoon and an awesome sunset, so that may be a factor, but I was pretty much blown away nevertheless. Also they have Geronimo, the world's largest petrified tree! Road trip nirvana.