Cameron Olthuis on link Building Blog informs that Google Adwords 'gather accurate data in regards to search volume and conversion rates for keywords.'
“Assuming that you already have a good idea of what keywords you want to optimize your site for you can take that list and enter it into your Google AdWords account. I recommend using a combination of both exact match and broad match.”
It helps finding out keywords which people are looking for and you didn't even think about it.
Checkout the full post.