The post I've linked to highlights the nature of forms becoming useful wizards, and whilst I agree it serves this purpose extremely well, I think the advantage is most evident when applying this codebase to Ecommerce channels.

Wayfinding, signposting - call it what you will. All the evidence collated of users in the 'cart', show that highlighting next steps in a process is one of the most important factors in reducing drop-outs, and consequently, increasing conversion.

For those of you who have limitations on the design of your shopping cart, then I'd recommend using this Jquery example: and watch your conversions go skyward.