Making customers register before reaching the checkout is something that a lot of e-commerce websites are still doing, though some are beginning to remove this obstacle to purchase now.
In a blog post this week, Jared Spool has a great example of why this usability mistake should be avoided; a 'major e-commerce site' that added $300m to its annual revenues simply by removing the register button.
The unnamed site in question had previously added a form asking for shoppers' email address and password between the shopping basket and the checkout page, asking for previous users to enter their details from the last time and for new users to register.
This was enough to put off plenty of first-time shoppers who didn't see why they should have to register first, while plenty of existing customers couldn't remember details and were forced to go through the process of getting a password reminder or setting up a new account. Interestingly, it turned out that 45% of customers had multiple registrations on the site.
The simple fix of removing the register button altogether and giving users the option of registering during checkout produced a 45% rise in the number of customers purchasing and the additional $300m in sales.
Seems straightforward enough, and there are plenty of surveys showing that customers dislike having to register, but there are still sites that do this. For example, after pressing the proceed to checkout button from the shopping basket on M&S you get this unnecessary page:
I've also found this problem when looking at the websites of Asda, Next, Boots and Currys. Perhaps these retailers should take a look at such examples and see what happens to their conversion rates when they remove this obstacle.
UPDATE: Three years on from this post, plenty of retailers are yet to learn this lesson, and are still making users register before checkout.