Most popular saved pages and most popular tags are very rich for mining. This is the whole purpose for apps. like Del. Furl, Spurl etc.
NYTimes has figured this out by licensing Furl from LookSmart for use in their TimesSelect product. It's called TimesFile and is behind a paid wall. Management can enter the customers "file" and deliver ads pertinant to the customers taste.
They have a guy that saves everything he finds about travel to Fiji and they can bomb him with ads for travel deals to the Pacific Islands.
Forget the esoteric aspects of folksonomies it's about delivering ads and making cash.