I have heard of it.. It has a lot to do with content and linking. Google realises that people are working hard to get their sites to the top of searches on particular keywords, i am yet to hear what the protocols are for google on this topic but because its not actually an illegal operation in googles eyes, it is frowned upon!
Things such as content not being changed after a year because they are getting high search values will affect it, linking in other relative sites who ARE getting high ranks etc. The normal
SEO operations and some more.
What google will do is lower your site namely to the 950th position on the search however its not always 950 obviously, its just a lot lower than it was previously!
Its a good idea as it creates a fair playing field for everyone, rather than people who spend thousands on
SEO input and so on!
Anyway as far as i can tell thats what it is, hope it helps! So be careful!