It is sad to see Xmarks go - they are sending out a 3 month notice to users.However what is relevant to a Sphinn audience in this in-depth article are all the experiements they did with search queries for different types of data, and what worked with bookmarking data.You could extrapolate that to suggest that similar data would be useful to Google in a similar way from their own bookmarking features, and likewise Delicious for Yahoo.