Both customers and companies want a quick and easy checkout experience. From what I've seen, a big UX bottleneck at checkout is the billing and/or shipping address(es) because there are so many input fields per address.
The traditional way of typing an address is something like:
Street address: 123 main st
State: NY ▼
Zip code: 12345
Country: United States of America ▼
This is usually frustrating for me, because some addresses are "edge-cases" and don't necessarily fit into the format required by the web page.
And often, these fields are duplicated to populate both shipping and billing addresses. My question isn't how to prevent that duplication (there are "Ship to my billing address" checkboxes for that), but it's about reducing the number of fields on the form from 6+ to just 1:
Address: 123 main st #101, schenectady, ny 12345
(could be a small, multi-line textarea too)
Is it a more positive user experience to combine all the fields for an address into a single input field?
(I know what you're thinking: how can you use or standardize messy input? Don't you need to parse it in order to be useful? Yes, and we have a way to do that. See this post over at Stack Overflow on parsing freeform (single-line) addresses.)