You will find people complaining about AdWords advertising as very expensive and ineffective tool of advertisements. But the fact is that those people have failed to utilize the medium properly and hence they lost a good sum of money. This is true if you don't know the tricks of using AdWords advertisements then you will surely lose your bank balance and gain nothing. There is a misconception that you have to be the highest bidder of a keyword. So people emphasize on bidding keywords instead of improving other areas related to AdWords. Its not necessary that you have to get the top slot of the keyword campaign. Even if you remain in third or fourth position visitors will click your link if you can attract them with your advertising.
I hope you understood what I mean. I mean to say that while you go for AdWords advertising you must take care of certain things. First you must learn the art of pay per click advertisements. If you don't know the smaller tricks you will definitely lose money without any gain. For instance if your keyword is 'sports shoes' and this will come up in every search of sport shoes with other related keywords in broad match option. In that case you will have visitors to your site who won't buy your product. But they will click the ad to enter and then will come out soon. If it happens you will have to pay Google the bid amount for every click. So you see that you don't earn a single penny but you will losing more than $50 dollars a week in such miss clicks.
Thus I recommended that you learn the art of pay per click AdWords advertising and start your war fo bidding. If you lack knowledge on the subject take help of AdWords guidelines books or online articles.