Over the years I've read a lot of articles about where writers physically write. Alice P. Sheldon had three different desks: one for her non-fiction, one for her SF fiction written under the name James Tiptree Jr., and one for everything else. Ernest Hemingway had a standing desk. Stephen King has a large room with a skylight. And so on.
I went deskless in 2008. At the time it was to save space in my apartment, but now I have another reason: due to an injury caused by a hit-and-run drunk-driver accident three years ago, my upper back can only take so many hours a day of holding my head up. I can make it through the day job all right, but I'm better off in a semi-sitting position once I get home. I'm writing this with my head and back propped up on some giant pillows I sewed, and the laptop on my lap (or what would be my lap if I were sitting upright). Here's a photo of my usual spot at home, with the computer added in to show the entire physical environment.
One thing I don't do, and stopped doing as soon as I got my first laptop, is write longhand. I have report cards going back to Grade 3 proving my handwriting has always been terrible, and I'm tired of apologising for it — especially since I've been proficient at touch typing since I was thirteen. It's just as well now that I have the spine issues, because typing is one thing I can do quite comfortably in this position.
The one thing desks are wonderful for is spreading out lots of pieces of paper and marking them up. This activity certainly has its merits, but from what I've been reading in the blogspace, it seems like more and more people are doing their editing onscreen these days than previously. Tony Noland's posts about using yWriter are illuminating on the subject (although it sounds like he edits from printouts too). So was E.D. Johnson's recent Friday Flash .org post about writing on a mobile device.
Everyone needs to find their own writing space, of course. I'm just offering mine up as an example because I've read too many advice articles saying that writers need a special room (when I live alone?) or a special desk setup (in this apartment? not going to happen).