Some think that will hurt Netflix DVD by mail performance. Some pundits might be tempted to quip "more than Netflix already has done to itself?"
But there is a countervailing argument. One might argue that users who really "want what they want, when they want it," or who "want it now," already have shifted to online delivery.
Also, users who have DVD by mail plans can choose plans that allow them to have multiple discs out at once. Not too many users really will be able to watch so many discs that delivery actually becomes a big problem.
Slower delivery by the USPS won't help, of course. But it remains to be seen whether it harms the DVD by mail business, which Netflix wants to wean itself off of, in any case.
Most people I know who use the DVD by mail service only watch on weekends. They're just too busy the rest of the time.