Search Bistro have released some very interesting documents over the last few week. One in particular, a Spam guide for Google raters which includes ways to spot if a website is spam. The document only covers basic methods of spamming techniques but what I found more interesting was the explanation of what sites are considered spam;

"At first cut it may look like yet another thin affiliate doorway to Amazon or B&N, but bookfinder4u.com is providing a value-added service to visitors by offering a comparison of prices between different online merchants. Ultimately you will be taken to Ecampus.com, Half.com, Amazon or another affiliate online bookseller, but the fact that they have their own price comparison infrastructure is the differentiator."

This topic is covered at a thread on the Digital Point forums.