Basically AddressBooker takes a POST of contacts data in JSON form, and does stuff with it, where "stuff" is currently limited to merging it into your Google Contacts. (GMail, Android, etc) This was my experiment in learning GData, AuthSub, and App Engine a bit more.
Anyway, I then wanted to get my Facebook Phonebook exported to my Google Contacts, so it'd sync to my Android phone. I didn't see an export option in Facebook (maybe I missed it?), so I wrote a little GreaseMonkey script instead to automate the whole process:
If you have Firefox and GreaseMonkey, then click the above link and it'll ask if you want to install it. Install it, then go to your Facebook Phonebook
(And keep in mind I barely know browser stuff or Greasemonkey or Python or App Engine or GData, so patches welcome!... email@example.com, or Github)
Update 2010-06-06: Facebook's markup changed again, but I'm too lazy to go update the script. Patches welcome.