The offer stands for all Checkout users, regardless of whether you use AdWords. New users who sign up for Checkout are eligible as well.
Checkout, which was released in June, has met with adoption problems. According to two surveys by analyst company Piper Jaffray, released in August, 81 percent of online retailers say they won't implement Google Checkout. The reason: Retailers don't want to cede customer ownership to Google. And 10 percent of companies surveyed said that Google Checkout would provide Google with too much insight into their business, especially with regard to Google search-related conversion rates.
Delays in order processing have also irked Checkout users. And, some small publishers have told Google Watch that Checkout can be difficult to implement on their sites because of integration difficulties with existing shopping cart software.
Google continues to make improvements to Checkout in response to complaints.