Shield all day every day. Inferno, and even Hell mode to some extent, is all about defense. You can have all the DPS in the world, but it don't mean a thing if you are 1 shotted by every mob in sight. With Force or Prismatic armor, I get nearly 8k armor on my Wiz (thats nearly Barb like!), and that is with crappy gear. That being said, Act 1 Inferno is still very hard in my opinion, but I can't imagine doing it glass cannon style, which would almost be miserable for a power-house style player such as myself. Although come PvP time, the glass cannon build will almost certainly be the one to go with, as DPS and Life will probably be the dominant factors there.
Now, if this was the Demon Hunter, I would say don't bother with a shield, since it is virtually impossible to get your armor rating to anything meaningful that would mitigate damage decently. DH is pure glass cannon, and a poorly designed class in general. Even with Force Armor being nerfed, it is still a far better defensive skill than anything DH has and really gives Wiz the option of going glass cannon, or Shield/Tank style. I prefer the latter, and it really makes a significant difference in how well u can survive vs many mobs.
If you're using force armor the tough stuff will 3-shot you anyway, so little point in a shield.
I do keep my barb's sacred shield in inventory (only barb item I didn't sell to get budget for gearing up my new wizard, it did have str int and vit on it along with 28% block), and put it on for certain elites, such as ones that don't let me avoid their fire chains, and sometimes reflect damage ones that seem to drop my health too fast (I do have ~1500 life/sec, so only certain tougher reflect damage elites actually require me to swap).
For general use, though, I find a shield too poor of a defense compared to the damage potential of a good offhand. If you're having a hard time without a shield, try force armor bliz/hydra with teleport and mirror image and of course seeker missiles from off-screen. You'll probably do more damage than a shielded wizard with more damaging skills and live longer due to simply staying out of trouble. Of course, with decent gear in act 2 you can just use missile/orb to 1/2-shot trash and use improved archon with familiar and magic weapon to kill any elites in 5-15 seconds. Act 3, on the other hand, requires some crazy gear to do the same, but even there I still think changing builds is better than changing gear, at least when it comes to such an extreme change like using a shield.