Well, as I understand it, the M324 is being or has been discontinued by Shimano. Don't despair though, because they've introduced a new model, the A530, that I think is even better! Take a look at it in the picture to the right. You can see that the non-SPD side is a very different shape. This new pedal supports your foot with a large, cast aluminum platform, rather than the thin, wraparound steel cage of the M324. As a result, there's more surface area under your shoe, which is really nice if you are riding in a more flexible shoe. I did about 20+ miles today on a set, wearing a pair of Teva closed toe sandals, and they were wonderful! Much better support, and no sensation of the pedal "digging" into your foot. To top it all off, the M530 is lighter than the 324 as well. All in all, a great improvement to a great idea.
I'm trying to keep a few sets in stock at all times, but it's been tough... they seem to fly off the distributor's shelves the moment a new shipment arrives, so I'm guessing demand is high. It's such a nice pedal, I'm not surprised. Come on by and take a look sometime... I think you'll like them. I do!