In 2008, I worked on Boots.com. They wanted a single-page checkout with the trendiest of techniques from that era, including accordions, AJAX and client-side validation.
Each step (delivery address, delivery options and credit-card details) had an accordion panel. Each panel was submitted via AJAX. Upon successful submission, the panel collapsed and the next one opened, with a sliding transition.
Source: Smashing Magazine Better Form Design: One Thing Per Page