From the Blizz forums, we've done some testing:
Pets get Str, Int, Dex bonuses for armor, damage, dodge.
Pets don't block.
Pets don't get any Vit bonuses.
Pets get +resist bonuses.
Pets get any regen bonuses(spirit walk, blood ritual), but do not get any life on hit or life leech bonuses.
Pets get any %CC on items, so do their 'auras' burning dogs and big stinker.
So, from my testing in late hell, early inferno - one of the best ways to use them is as massive CC generators - if you're gearing for armor, resist, regen, int and str / vit - try to get as much CC on your items as possible, and with 5 extra guys hitting enemies, you can get a lot of CC out quick.
The problem of them surviving ACT 2 Inferno still remains - without some sort of life scaling, and with less insta-gib inferno-ness, I just can't see how to make them useable for end-end-game.