The pricing doesn't seem all that great. Take $7.99 per month for 1 DVD out. That equals to 8 DVDs rented for one of those DVD rental boxes in a grocery store (RedBox, BlockBuster) assuming you return them the next day. In order for you to rent 8 DVDs in 30 day month, you have to be getting new DVDs every 3.75 days.
So basically, in order for it to equal the cost of a comparable product, you have to get the DVD and watch it the same night, then ship it back and hope 2.75 days is enough for Netflix to ship you another one.
Don't know about others here, but I don't really get time to watch DVDs during work days. This leaves the weekend, so for $8 a month, I can rent 2 DVDs per weekend and receive greater amount of entertainment during a more convenient time.
So using your example of 4 DVDs per month, that's $2 per with Netflix or $1 (50% less) per with box rental services. So in terms of actual spending, you are still only saving 4 bucks (not even a cup of coffee), but % wise, you save 50%.
(and yes, I go to the store regularly, so I'm not counting cost of gas in this example)
Now, if they only had the latest stuff in the streaming catalog... that would be entirely different story.