As the market stands at present, few potential employers know what CIW is, and even fewer are impressed by it. Your best bet for getting hired as a web designer/developer is to have a good portfolio, and be able to demonstrate a range of skills. If you don't have this, then all the certificates in the world aren't going to make a difference. If you do have this, then you won't need a CIW.
That said, the CIW course involves teaching the student about some aspects of web design and the wider Internet, and as such can be a great primer for someone interested in beginning web design.