Well, it happened (sort of). Another group recently published the results of an experiment we are trying to do in a prominent journal for our field. Now at first, I was upset about it, given that this experiment is the core of one of my student's PhDs. It is really easy to see this work in print, and get all freaked out.
Taking a second look, I found that Namnezia is totally right about scientific scooping (in my decidedly not crystallography/single answer field). Our experiment is similar in broad outline to what has been published, but the details vary in some very significant ways. Yes, we may be second, but at least we have had our thinking validated! First of all, this is an interesting scientific problem--at least one other good group is working on solving it. Second, our original intuition has been confirmed, demonstrating that our GENERAL approach will definitely work (which wasn't at all guaranteed). I am also hoping that a little competition will be motivating, but on that one, you never know.
Now, I would certainly have been happier to be the first to demonstrate this concept, but the sky isn't falling, this didn't wreck my tenure chances, my student will still get nice publications, and all our hard work to date isn't wasted. In some ways this is new to me (much of my prior work was on REALLY niche systems or in systems with a relatively high barrier to entry). I am actually pretty happy to have more scientific playmates now, so to speak. But everything is a mixed blessing, so working in a more populated area of science means things like this are going to happen.
Our approach has a different set of advantages and disadvantages than the one already published, so I still think our project will produce some interesting new science. Fortunately, being first doesn't really matter all that much in the grand scheme of things.