I think the quest to find extra-solar planets is amazing - and partly because of what can be learned about the stars, and how stars formed, along the way. As Mitzi said, looking at the changes in the light helps figure out if what's making the star's light dim is a planet or a "star-spot". From the posts and information on sunspots, you know that these spots are the locations of strong magnetic fields. These magnetic fields also change the light coming from the star, so one of the ways to rule out the dips as being due to star-spots is to see if there are indications of magnetic fields. And in doing so, we learn about the star itself!
Also, learning about how many Jupiter-type planets vs. Earth-type planets, and where they are (how far away from the star do they orbit?), and around what kind of stars, tells us about how stars and planetary systems formed in the first place. Are we 'weird' to have rocky Earth-like planets? Are massive close-in orbiting Jupiter-sized things more normal than what we have? Do only certain kinds of stars have certain kinds of planets? These are all questions that we can really start asking now! (And, even if the answers to those questions create other questions, well, that's science. :-)