First you'll need to head to Postable.com and sign up for an account. Hopefully OAuth support will be added in the future to make this even easier.
When you're done signing up, a new page will load with a pop-up displaying the link you'll share with people whose contact information you want. You can click the copy button next to the link, and it will copy something like this to your clipboard:
Please click this link and enter your contact information -> www.postable.com/yournamehere
After a contact edits their information, they will be given the option to sign up for Postable. This isn't necessary, but can be useful to you and them if they decide to fill out their profile area. When a user updates their profile and changes their address, phone number, and other information, it will also update across all of the Postable address books they are a part of. The same goes for your own information, if you choose to provide it. This is great for someone who travels a lot or never stays in the same place for too long.
Once you're satisfied with the amount of information collected in your Postable account, you can export the entire list to Excel or CSV format for Gmail, Outlook, or Apple Address Book. There's even an option to print labels if you so desire.