Just spent an hour working out how to output a list of contacts from a web application in the correct format so that it can be imported into the address book in Apple OS X.
It's basically a simple text file with the values separated by tabs and each distinct entry separated by a new line. The clever bit is that by using the first line (which might normally be labels in a file exported from a spreadsheet) to indicate the content of the subsequent 'columns' of tabbed values, you can give address book a clue as to their content, so that it imports it correctly.
The labels I've found to work are as follows:
first - N.B. it does not seem to respect localised address formats like '
middle
last
prefix
suffix
nickname
address (home) street
address (home) city
address (home) stateaddress (home) county' or 'address (home) postcode'
address (home) zip
address (home) country
phone (home)
url (home)
email (home)
jabber/icq/aim/msn/yahoo (home)
note
Obviously you can change the value of (home) to match your requirements - i.e. phone (work), address (other).