NPR had a couple of good stories on front porches and their come back this week: Sitting on the Porch: Not a Place, But a State of Mind and Porches Knit Together New Urbanist Communities.
I love porches in all their variety. My parents (who still live in the house that I grew up in, which my grandfather built in the late 1920's) have three porches: a front porch, with chairs and ferns, where my father used to smoke cigars and watch the neighbors; a screened-in back porch, where we used to eat dinner on hot summer evenings; and above the back porch, the sleeping porch, a wonderful room with knee-to-ceiling windows on three sides, surrounded by trees. I remember being excited when my brother went to college, because then I got the sleeping porch all to myself. Waking up on the sleeping porch as a storm blew in was particularly exciting - cranking twelve old casement windows closed as lightning flashed and rain blew at you really got the adrenaline going.
John Richard Lindermuth blames the loss of porches on the advent of tv and air conditioning. I think that a preference for decks (mostly in the back of the house) might also have something to do with it. Anyway, here's a neat photo essay: The Evolution of the American Front Porch.
Edited on 4 Aug 2006 to add another cool link: The Rise and Decline of the American Front Porch, from the Montana Heritage Project. This author ties the rise to transcendentalism and increased interaction with nature (along with architectural pattern books), and the decline to a loss of community and car exhaust. Maybe.