Interestingly enough, the larger trend in business is to pay for performance now.Contractors get brought in to work sites, are paid only for the hours that they work, and are cut when they cease producing (in theory).
Artists and programmers are frequently contracted to create a product while they work their own hours at home, and they are paid only for their final product.
Laws such as this one in California will only serve to accelerate this trend.
Why take on the growing burden of a new "employee" when one can pay a fixed amount of money for a final end-product, after all?!
Thus, labor unions will see their membership numbers suffer as businesses find alternative ways (instead of using employees) to obtain their desired results.
Home-owners are already doing this. Who among us pays a plumber for the time that he spends caring for his family? No, we only pay him to fix our plumbing. We aren't going to pay for his time away from our home.
Likewise, businesses are going to find ways to not pay for the time that emplyees spend at home, even if that means no longer hiring employees but rather using contractors and other outsourcing methods.