Today Google has added new guidelines for webmaster to make there website good for users and search engines
Google Says follow are bad links or fall in Link schemes
Text advertisements that pass PageRank
Links that are inserted into articles with little coherence
Low-quality directory or bookmark site links
Widely distributed links in the footers of various sites
Forum comments with optimized links in the post or signature
Google is of the opinion that updated guidelines will give you a better understanding of how to create and maintain Google-friendly websites.