Most SEO geeks will have Matt Cutts from Google towards the top of their list of people to follow for SEO news and information. He said something very interesting recently at SXSW about Google introducing a filter/penalty.
Matt never gives everything away during changes but it is clear that Google are in the process of making updates that may affect many sites and may leave a lot of spammy SEO consultants looking over their shoulders. Webmasters and consultants who are over optimising sites may find themselves being spanked with ranking penalties. Those with great original content that is regularly refreshed and well-structured will see the benefits.
It looks as though Google are punishing over-optimisation. Matt mentioned Google don’t have anything against SEO, they have something against spamming which they aim to penalise.
If you are writing content with keyword density above 15% and adding the same keyword in every alt tag, meta tag and titles etc across all pages you may not be doing yourself as many favours as you think.