With another new e-commerce venture I am a partner in, after spending nearly $300 in PayPerClick (in 1 month) with 3 engines: Enhance, Google and 7Search, as well as another $100 with PPC deals at AdBrite and AdEnage networks, I can state that it didn't really work for us. And we managed to bring close to 6,000 visitors in July.
On top of that, I am VERY displeased by AdWords service. Not only it is incredibly confusing, they were always finding reasons and putting our keywords on hold and then disabling them. 3 times I've tried. All failed. I can't stand it anymore.
This was, however, my first PPC experience. I guess you have to really know what you are doing. I thought I did (I did everything by the book and I was generous by targeting popular keywords, as well).
However, it shows that it works for most people and I might have fallen into the "exception" category.
For the Pay Per Click to work first make sure the keywords you have selected are relevant and link to the particular page which contains the information a person is looking for. The pay per click advertising seems expensive form of advertising and the sales conversion by PPC is also very low but it all depends upon you how you are going to monitor it and going to implement changes if required to increase the conversion rate. If you're getting atleast 2 to 3% conversion rate in starting point it can be considered good start.