But isn't bypassing DR a benefit to attack? If you don't have any enhancement that round left because you've used the special ability of your weapon, I don't think you should be able to bypass DR that round. Doing this makes Defending much more powerful than it is -- I can make it harder for the baddie to hit me, but I can bypass his supernatural defenses with ease? Where's the trade-off? I know it's a magical weapon, but that is a little more powerful, that what I remember, if it is adjudicated the way some of the above posters are positing.
However -- I agree with the sundering bit. Even if you've transferred all your enhancement bonus to AC that round, the weapon is still "magical," and only a magical weapon of requisite power can sunder another magical weapon. Transferring the enhancement bonus shouldn't effect the weapon's power level for this purpose, IMO -- the situation is one of defense (resisting a sunder attempt), at which this weapon excels.
