The latest blog post of Matt Cutts of Google is a Questions and Answer post.
There he answers a lot of questions including the RK parameter and gives a lot of valuable info for an SEO:
Here:
http://www.mattcutts.com/blog/q-a-thread-march-27-2006/
Thanks Matt.
EDIT:
Some more info about his post:
http://www.seo-scoop.com/2006/03/30/tidbits-of-google-knowledge/
http://www.irishwonder.syndk8.co.uk/2006/03/29/matt-cutts-selected-quotes/
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i love all the techniques used by matt cutts i would really like to use his tactics