clipless will make your sprinting and acceleration a bit easier. Once you're up to speed I seriously doubt you could tell the difference. For longer distances you can run into issues w/ hot spots on your feet as well. It DOES feel faster, no doubt about that -- I loved it until I had to switch back to platforms due to comfort issues. Then I realized that the improvements were coming from the engine, not the gear. If nothing it'll be a great learning experience as to how it should feel to be connected w/ the bike, and it WILL improve your pedaling on platforms.

If you're a true skeptic, make liberal use of REI's awesome return policies. It does feel great to use clipless -- just don't toss the vanilla pedals you got w/ the bike away.