From George Dinwiddie (interesting blog, BTW) on the ScrumDevelopment list comes this great article: Resistance as a Resource by Dale H. Emery.
From the article:
You gather your courage, call people together, and make your proposal. From your right, Charlie says, “But we tried that before, and it didn’t work.” To your left, Pam says, “But we’ve never done that before.” Right in front of you, Lee says, “But that’s no different form what we’re doing now.” From the back of the room, you hear a rising chorus of, “But we don’t have time!”
You don’t really have to imagine this scene, do you? You’ve lived it. Perhaps you’re living it right now. You’re getting resistance. Now what do you do?