Qwikster will rent you DVDs and Netflix will rent you streaming movies. Two separate sites/companies, no interop, you have to sub to both separately, etc. Here's the explanation from Netflix CEO Reed Hastings. This seems amazingly dumb at first blush. (ps. Qwikster?!!)
Update: This is an excellent level-headed analysis of the deal from Dan Frommer.
Netflix's holy grail is to get each person, not each household, to have a separate streaming subscription, the way everyone also has a separate Facebook account. Separating a per-household service like DVD rentals-by-mail helps simplify that eventual transition.