I voted "other", namely the crack-addled weapon familiarity drek. I don't think it'll have any notable impact on game balance or anything, it's just absolutely [stopping my thought now].
A close second would be the Paladin's mount. Granted I haven't seen the books, yet. But if it involves teleporting, summoning, extraplanar/non-planar calling, or anything more magical than being able to whistle and have the mount come, it's a bad idea. Okay, maybe I should have voted the Poke-mount. Honestly, calling this one crack-addled is a grave insult to non-functioning crackheads everywhere.
On the other hand, I'm quite eager to see the new DR rules in full. I've used something reasonably similar since 1E and haven't bothered to update things for 3E yet (with the bypass damage). The 3.5 DR promises to save me a bit of work. As far as _why_ I like it, I think that having DR that any single character/weapon can always bypass is silly. If it never comes into play, then why bother having the mechanic at all.