Dude, Where's My Dude? Dudelicious Dissection, From Sontag to Spicoli by Ron Rosenbaum : Dude, this is some seriously funny reading. The complete history of Dude, from its humble origins as a "aesthetic craze" in New York, circa 1883, to Dude, Where's My Car? in 2000.
Everybody thinks "dude ranch" came first and was somehow the origin. But whence came the dude in "dude ranch"? Before the dude-ranch dude there was dude as dandy, the dude as an urban aesthete; it was the urbanity of dude that made the dude-ranch dude dude-ish.
This is so stupid, but its a smart stupid. Almost Pynchonian, really. Seriously, its a surprisingly complete article, worth reading if only to experience the whopping 160 or so occurrences of the term "Dude" or its derivatives. [via Ipse Dixit - Thanks Dude!]

Update: Unrelated, but interesting: A brief Googling of Pynchon and Dude turned up this article, also by Rosenbaum, about Pynchon and Phone Phreaking.