Some economists believe that banning such agreements could harm Silicon Valley's open, collaborative model.
If the existence of an agreement isn't disclosed to the employees, then the model is not really what it is always held out to be, but something more akin to private industrial policy. I don't believe this is any better for consumers than for employees over any length of time. I've personally felt (as a consumer) that tech & internet development have stagnated in the last year or two, notwithstanding the existence of new things; perhaps this is why.
Settlement or litigation, this is probably going to set off a wave of cross-hiring because firms will no longer have the security of the agreement in place when negotiating employment agreements, and turning away a candidate from another firm with good skills may look suspicious. Good for engineers, good for the local economy, probably good for innovation; not so good for CFOs and CIOs who like sleeping at night.
I'm guessing companies will settle rather than fight; but if not, it'll set off a sector-wide feeding frenzy in the market. This should make the rest of the year interesting. It's partly political, to be sure, but slow wage growth in a period of generally rising productivity per capita has been a source of discontent for quite a while now. There is a lot of pent-up frustration, and also a lot of companies sitting on cash reserves in search of a market signal; neither situation is sustainable.
Incidentally, Microsoft, IBM and Genentech are all said to be in the clear.