This may be risky, but I wonder if it is possible to draw a line connecting two conversations happening at the moment...
Point A is the discussion between Dan Green and Derik Badman about what is or isn't literary constraint.
Point B is the recently-created Mundane SF Blog and the various conversations the whole concept of a Mundane SF movement has sparked.
In the Asimov's forum discussion, Jack Skillingstead makes a parenthetical remark that begins to chart a course between points A and B: "Not a bad idea in terms of a story telling net (if you try to play without a net the game gets sloppy; other nets: viewpoint/ wordcount/ beginnings-middles-etc.)"
Robert Frost once suggested that writing free verse poetry is like playing tennis without a net (wouldn't that be racquetball?), and many writers create nets for themselves of some sort or another, a way to limit the infinity of possibilities that a blank page suggests. Constraints are, obviously, one way of stringing up a net or two. For science fiction writers, the Mundane movement offers a way to limit the possibilities before the work begins. This may be useful, perhaps even necessary.
The question becomes, then, how important are such things to readers? I know plenty of people who couldn't care less what constraints authors pose for themselves, any more than they care about whether they write on a typewriter or with blood pricked from their middle finger. The final product, the written work, is what matters to most readers. The constraints can be interesting to discuss, interesting to philosophize and theorize about (and Derik has proved this with his MadInkBeard weblog brilliantly -- I thought it would be interesting for a couple of days, and I have found it to be consistently interesting for months now), but the work itself is the most compelling focus.
Mundane SF is a little different, because there probably exists more of an audience that wants most of its literary diet to be science fiction that is plausible or near-future than there is an audience that wants most of its literary diet to be works written under specific constraints, restraints, and frustraints (although the New Formalists might make up a good part of that audience).
My own feelings about both the idea of constraints and the idea of Mundane SF is basically agnostic, although the agnosticism is mostly overtaken by indifference. While I was tempted to say, "Whatever, man, just so long as it produces, like, good writing, y'know?" I'm entirely aware that "good writing" is an almost uselessly subjective term. Many movements claim their way is the only way to write "well" -- a claim that, thankfully, the Mundane folks have not made. I realized after more thought that while I find constraints interesting to talk about, I'm not much interested in Mundane SF as a topic, a confession I am a bit wary of making because many of the people who have allied themselves to the cause and drizzled on the barricades are writers whose works, on the whole, I very much enjoy and admire.
My problem is, I just don't care whether fiction is plausible, realistic, or believable. I want it to be imaginative in as many ways as it possibly can be, because I, personally, will forgive almost anything else if there seems to be a unique and powerful imagination behind a particular piece of writing. Frankly, any movement that excludes Cordwainer Smith is not one I want to give much time to, whether it be the movement of the Literary Realists or the movement of the SF Realists.
Constraints in the work of Cordwainer Smith -- now that's an idea I'd be interested in pursuing...