They screen sites that want to show their widget, so they know ads are going to be on good sites. They let advertisers choose institutions (eg Stanford) or com

They screen sites that want to show their widget, so they know ads are going to be on good sites. They let advertisers choose institutions (eg Stanford) or companies (Google) to target and then targets ads based on IP addresses. And the ads work very nicely - instead of leaving the page, you get a lightbox so you can go right back to your page.