I have a concern with "proof in geometry" discussions that takes a slightly different direction than several of the recent posts.
Geometry is not a course in proof, but proof is essential to the development of geometric understanding. The concepts of "statement-reason," syllogisms, converses, inverses, contrapositives, truth tables, are not unique to geometry. In fact proof is just as essential in algebra, or calculus, or elementary school arithmetic as it is in geometry. Let me re-state to be absolutely clear: Proof in geometry is important. Proof in other courses is also important.
The level of formalism will, of course, be adjusted to the mathematical setting. Proofs in graduate courses in topology are very different from reasonable and reasoning arguments presented to third graders as they learn multiplication tables.
One of the difficulties in my own high school experience back in the late 1950's was that proof, reasoning, even defense of an idea, was seldom raised until the geometry course. I'm delighted to see reasoning and proof as one of the "Standards" in the NCTM Principles and Standards IN EVERY COURSE.
Steve Cottrell Mathematics Supervisor K-12 Davis School District P.O. Box 588 Farmington, UT 84025-0588