I agree completely with Ken! We use Uniform Extents and don't reorg unless we get ~1000 extents. We use size 128K, 4M and 128M extent_size tablespaces. We have seen some improvement in performance, but mostly we save because we don't have "unusable" space in our tablespaces. Everything is reused.

For a good article on this and how to implement, please see:
http://otn.oracle.com/deploy/performance/pdf/defrag.pdf or article "How to Stop Defragmenting and Start Living" at http://www.hotsos.com/catalog/

Good luck!