Normally the big "where to show your ads" decision is between the display network and the search network.
Search partners are hundreds of non-Google websites (like AOL), as well as Google Maps, YouTube and other Google sites. New campaigns default to show ads on both Google search and search partners.
We check the campaigns we manage regularly to see how much each conversion costs (a sales lead in in our case) on Google search versus what it costs on search partners. Most of the time they're about the same. Sometimes the difference is huge.
In the last two weeks the cost per conversion on search partners almost doubled on one of our campaigns in South Africa: R85.41 per enquiry on Google search vs. R164.06 per enquiry on search partners.
The campaign makes sense even at R164 per enquiry because each sale is worth much more than that, but disabling search partners and showing ads only on Google search frees enough budget to fund an extra 60 enquiries a month.
Decide where your ads show using the 'Network' setting in Google AdWords. Screenshot below.
You can compare the performance of keywords, ad groups and adverts across the different networks by segmenting the stats. Click on the 'Segment' dropdown and then select 'Network (with search partners) as shown in the screenshot below.
Give me a yell if you need a hand checking how much your search partner enquiries cost.