eBay's new Checkout feature will begin appearing on the site today. eBay warns that this feature represents a substantial change to its infrastructure that may affect systems in other areas of the site. Checkout allows buyers to complete transactions automatically at the end of an auction. It is available for any single item on eBay, including auction-style listings, Buy-It-Now listings, and Store fixed-price listings. (See October 2nd Newsflash.) The rollout has already caused problems with third party vendors who launch to eBay.
http://www.auctionworks.com/announce.asp
http://pages.ebay.com/checkout/faq.html