Link Incest linking web sites together containing the same Class C - block IP address, or subnet address is seen as link Spamming by some search engines according to some SEO Services http://www.ip-report.com/index.php
Some SEO's have been saying that for years, but Google (Yahoo, MSN, etc...) have never, to my knowledge, made a statement about this. In the absense of any sort of corroborating evidence, I believe it is irresponsible to make these claims.
Not quite true. Google wrote an article about it... http://www.cs.toronto.edu/~georgem/hilltop/ This doesn't mean that it is in fact being implemented, just that Google clearly has thought about implementing it.
It would be easy to test though... three servers and four domains... server a has page m and n under one domain and page o under another, server b has page p and server c has page q m and o link to each other with obscure search term nobody uses. n and p link to eachother with same term. q is used to provide a neutral link to o and p that the spiders can follow... then sit back and compare results? I can provide server a with a couple of domains...
I have for the last 6 months only been linking to seperate C- Blocks. I personally believe that linking within the same C- Block discounts the link and also puts you at risk for keyword spamming if you recipicate with those websites and using the same anchor text for most of your links.
I can not speak to the first two components of that theory, but I believe I can speak to the third. I wrote a server-side script which dynamically created semi-random link text for my site-wide links and the results appear to be nil. You can see the script in action in the lower left hand corner of the Internet Search Engines FAQ.
I'd like to ask like Weirfire what a class C means? Lever - I tried to follow your "this" link to find out but the link is broken. Are we - like other website designers - at risk because we have a copyright notice with a link back to our website at the bottom of each website we create? Do we have to vary the anchor text?
I'm not sure if calling it 'spam' is accurate. Isn't it only natural for an individual or company to link two or more of their websites together for reasons other than seo (dare I say, traffic..).