Sure, account-binding items/gems prevents the duplication problem. However, it takes away from the game play that I've enjoyed for over 15 years of my Diablo 1, 2, and 3 experience. Except for Hellfire ring crafting ingredients, portal staves/ingredients, keywarden keys, etc., nothing should be automatically account bound.
With the understanding that duping DOES and will continue to occur, fixing THOSE problems and identifying the responsible accounts then banning them should be the number-one priority. If money is the name of the game, then hey guess what: that person who violated the terms and conditions of the game has to BUY another account in order to play! Yay! Right? More money and less incentive to cheat.
I have a [partial] solution that I hope you'll consider: In past games played (Guild Wars in particular), we (the player) had the option of customizing single items at the cost of rendering the item character (not account, but CHARACTER) bound (please never do character binding, account binding is perfect) and in return we received a small bonus like +20% weapon damage (the Diablo 3 equivalent would be something like +10-20 damage or something small, yet noticeable). To take it one step further, you could create this same option for armor / offhands and give us choices like +xxx armor, +xx resist all, +x% crit chance, etc etc. The player benefits from the additional statistic and it provides security from having their items stolen. It also reduces the likelihood of peoples accounts wanting to be hacked / stolen for their items (yes, I have an authenticator already to help prevent that, but that's not my point).
I hope you'll reconsider the account binding situation. It really hinders your players'/fans'/customers' gaming experience. I've personally spent probably over $2000 on the real money auction house, but had I known the game would run into situations like this, I probably would have rethought my actions more clearly.