The only complaint I would have is that they sometimes don't come in the order you want... Other than that I think it's great. Especially if you watch a LOT of DVDs. Even on the one DVD plan, if you check "returned" the day you get the DVD you get the next DVD the next day... so you always have at least one DVD lyring around the house.
Netflix is fantastic. They're very quick, I can mail a movie back to them on Monday and I have a new one by Wednesday. The DVDs are almost always in great condition (I've only had one that wasn't) and you can choose the order that they arrive to you in. Besides the fact that it's cheaper ($20 a month = 4 DVDs at Blockbuster but as many as you can watch with online services).
So yes, IMO, it is very worth it.