I have mixed opinions on this one. I appreciate the auto populating of City/State when you first enter the Zip. By doing that first, the suggestions of typing in address/street could be a much more accurate list as you've already filtered by state/city. The ones that come up with options from other states when I type in 1234 Main St will give me a list of pretty much every state/city in the country.

This feels like the physical equivalent of email validation, though it's harder to properly validate.

Similar to email validation, I've definitely seen people get bit (or, well, their customers getting bit) by people making untrue assumptions about the acceptable form of an address. See: a number of products that can't be ordered for USPS General Delivery simply because the address form won't allow it.