Those just made the extractors not require drones, right? I had the vespene efficiency talent (+25% collection rate) but never really had to worry about having too many drones or whatever. As to the mutalisks, I used them occasionally, but they seemed a little fragile for my tastes. I did, however, read that you can bunch a ton of them up in one spot and use Kerrigan's "double damage for 8 seconds" ability on them, which I will definitely have to try at some point. I imagine a couple dozen double-damage mutas would be dangerous indeed.