The latest edition of Mac Daily Journal (1st page as PDF here) reveals that Safari 3.2’s anti-phishing technology relies on downloading a database of prefixes of URL hashes from Google to check against your current URL, using the Safe Browsing 2.1 protocol. If the match is positive then a full URL hash is requested from Google.
Not that Apple mentions this anywhere, nor has stated a related privacy policy about what Safari sends to whom.