As some of you may recall, I'm decidedly in the flat pedal camp. While I may not agree with Beng entirely in his post, the fact remains that so far as efficiency and that mythical power on the up-stroke legend... well, there's plenty of evidence that is hyperbole. The real benefit, as I see it, are keeping the foot in constant contact with a specific location on the pedal. A lot of people feel more secure with this. If that's what you're looking for, then ya, try them out. If you are under the mistaken impression that you will magically cut your time on a given route by 10%, then save your money for something else.
I did try both the SPD and Look variations on my bikes for a couple months. I never got comfortable with them. In fact, I just did not like them at all. I'm pretty happy with regular flat pedals. But I know I'm in the minority here.