My new occupation is requiring me to learn a good deal about laundry soaps and detergents. I'm sure you may be skeptical, but it's actually quite fascinating. To make a long story short, I'm going to argue that you should never, ever put woolens in with the regular wash, no matter how 'superwash' your yarn might be. (This has nothing to do with the action of the washing machine, only the detergent itself.)
Here's why: laundry detergent isn't just soap. Besides the cleansing agents, I've learned that detergents contain stuff called 'binders', and sometimes contain enzymes. Binders play several roles in the laundry process. They keep the cleansing agents from clogging your washing machine and building up on your clothes, but they also help keep the water soft and they raise the pH. The cleansers work best in soft, alkaline water, with a pH of about 9. Some enzymes, although they are not as popular in our detergents, may decompose proteins.
So what do we know about wool fibers (and other animal fibers) that makes this information important? As a protein-based fiber, wool prefers an acid environment. That's why you're often instructed to add a splash of vinegar to the last rinse of a wash, and why acid is used to bind dyes to the fibers.
Now, I have to admit, I've been reading about detergents for less than a week. But I've got to think that detergent can't be good for wool, as it produces a consistently alkaline environment when wool needs a more neutral, or even acidic one. I don't think I'll be putting my superwash socks in with the wash anymore.
(Yep, still working on that lace. I've got two repeats, and still have lots of good knitting time today... I'm planning on a repeat a day if I can manage it.)