Site targetting has arrived

Google has finally launched site targetting for adwords.
In order to enable the site targetting option you need to go into your account settings after logging in and toggle the option. You then have the option of choosing between normal ads and targetted ones when you create a campaign. Unlike with the normal ads you then have to specify a CPM rate.
So how do you choose sites?
You have two options. You can either specify specific sites that you know are in the network or use keywords and then choose from the sites available that Google considers to be relevant.