A few hours later I noticed my spending stopped completely. I went back into that campaign and noticed that all of my ads had been disapproved. I knew my ads had stopped because I only had about 3 campaigns running at the time.
If you, like me, often have 10 or more campaigns running, and you like to create a lot of ads for each campaign, Google has a feature you'll like. If you go to the Tools menu and click "Disapproved Ads" you'll see all of your disapproved ads, and the reasons the were not approved all on one screen.
This is helpful if you actually want those ads to run and make you some money.
The reason my ads had stopped was because the landing page I was sending users to had a popup. I didn't notice the popup because FireFox automatically blocked it. Keep an eye on popups for affiliate campaigns and use a browser like IE to make sure you can tell if there are popups.
