Actually, you don't explicitly allow Google to import the data. Google does the following:
a) scrape Facebook.com;
b) notice that someone named "Roderick Evans" on Facebook is friends with someone named "Danielle Benson" on Facebook;
c) notice that someone named Roderick Evans' GMail account has someone named Danielle Benson in his contacts;
d) they're done. Your permission is not part of the process.
Your Facebook identity is now associated with your Google profile, and your Google profile gets associated connecting edges, without your permission or notice. If by some miracle you swing by your Google profile, and you notice that your Quora/Twitter/MySpace/Facebook accounts have all suddenly been connected, you can sever them, but I received no notice of the connection beforehand.
At least, that was how it worked for me before I deleted my Google profile. It's described in more flowery terms here: http://www.google.com/support/websearch/bin/answer.py?answer...