I ran a Google AdWords campaign last week and I have to say I was surprised by the results. I built up an ad for the Blog Oklahoma Podcast and set a limit of $5 a day. With Google AdWords you pay per click. So your ad could be seen thousands of times, but you're only going to be charged if someone clicks on your ad.
To over simplify what goes on, an ad placement is based on the keywords you defined and those keyword slots are auctioned off (how I don't know yet). You set a bid limit for those slots. I originally set a max bid price for $2, but quickly burned through my $5. So after some research I knocked that down to $.30. The higher the bid the more likely you'll show up on the first page of Google search results based on your keywords, but with the lower bid I was able to get more ads shown for my low $5 per day limit. What ever your bid on that ad slot was is what you spend when someone clicks.
So from Wednesday afternoon to Monday morning I spent $25 on my little AdWord campaign. And believe this or not, I doubled the average traffic to blogoklahoma.net. Saturday performed very well compared to Thursday, Friday, and Sunday (I lowered the bid on Friday morning).
The first thing I did this morning was pause the campaign so I'm not spending any more money. I'm not going to remove the campaign yet because I want to dig through all the stats first.
After I get the podcast going again later this month I may launch a new campaign. I ran this test when I wasn't putting out any new content, so there's that to consider.