We are currently under going a re-design in a a sign up process for getting your house connected to electricity and natural gas.
The first step asks you to enter your address in a number of fields as shown:
In an effort to reduce steps and space in the sign up, the suggestion was made to integrate an auto complete feature such as this:
Which method of entry is more effective and optimal for the user? and what are the pitfalls of converting to an autocomplete widget over manual entry? Initial usability testing has shown that from a group of 100 users, 60 users preferred autocomplete, the other 40% preferred manual entry.