I've been messing with Shiftry Ex (CG) on and off this season. It has really nice all around stats and a really nice Body to discourage rampant poke power use. The main downfall is it's a Ex card with two double weaknesses. One of them being Fighting makes it even worse. If Magmortar (SW) never arrived you would probably see a lot more speed Grass decks around, but that's not the case so the Grass weakness doesn't really hurt too much. Dark Eyes looks better than it plays as a tech card. With the additional HP the DP series cards have, an occasional 2 damage counters (that your opponent has control over) doesn't hinder most decks enough. If you want Dark Eyes to have a game changing effect you have to focus on Shiftry and get 2-3 out early in the game. Needing 2-3 Shiftry Ex (CG) out early changes Shiftry Ex from a tech line to at the least a support line or possibly the main line (which is very risky now). About the only thing I can see Shiftry Ex working in as a tech is something that can stall the game out allowing Dark Eyes to make a lasting effect on the game state.
By the way, I did play Shiftry Ex with G&G during states and found that I couldn't get it up fast enough early game (Gardevoir and Gallade always should take precedence) and late game it did too little or nothing (my Gardevoir using Psychic Lock). I also found I could very rarely, if ever, risk bringing it into the active role to attack, because of the double double weakness and losing 2 prizes to boot.