I've given up on more than one message board because it grew to the point where I could no longer reaonably stay up-to-date. It would be nice if LW didn't develop the same problem.
That said, this seems like a hard rule to enforce, unless we happen to have fewer than three people wrting posts. I was about to say "how do we decide which three posts should appear" and then I remembered that that's what voting is for.
If this 'explosion' is temporary, I have no problem dealing with it for a few days or weeks. This is the time when LW is still new and exciting and everyong will be willing to read two dozen posts a day. By the time the novelty of reading has worn off, maybe the novelty of writing will as well.
I think that three posts a day over and above Yudkowsky and/or Hanson posts might be enough. Where anything that gets voted to 0 or below doesn't count, nor do quick links.
Say you differently, readers? I'm just trying to space things out so we don't get overloaded with everything, all at once... if it turns out that people just have more to say than this, sustainably in the long term, then we can raise the posting speed.