Is anyone familiar with how Google considers IP when determining the strength of a link? Say I have 3 Golf Club websites and I interlink them on the same dedi with the same IP, is Google going to consider those links as strongly as they would if they were coming from a different IP? I'm sure the answer to this is no so my actual question is how much does it effect the strength of the link? Does it lower the relevance value of your link, the link strength or both? Also, where does the line get drawn? Is 126.44.201.101 treated completely different from 126.44.201.102 even though they are clearly from the same host?
This subject comes up often. The general thought seems to be that similar IPs are devalued. There is no hard evidence of this, however, and at worst, they'll be treated as no value, not negative value. My personal opinion-- for what it's worth-- is that a few might be fine, but if you get too large a percentage of your links this way, they will be devalued.
what about domain registration? Say I set up 3 related websites on 3 seperate hosts and interlink them, can Google tell I own all three of those sites based on the domain registration?
I'd have to do some research, as I've never dealt with a scenario like this before... But my initial reaction is that yes, Google probably has a way to find out. If whois.com can tell me you own three domains and the IPs associated with them, I'm sure Google can, too. It doesn't sound like you're abusing this as a link-building tactic, so I wouldn't worry too much about linking your three sites. As long as you have other quality links, I have to believe this will count as positive juice. I've seen companies getting positive juice from their different top-level domain sites like this. (i.e. mysite.co.uk passes juice to mysite.com, etc.)
If you are doing these to inter-link different language websites or slightly different topic sites (say each one sells different golf products) I don't think that Google would penalize you for serving your visitors more related content from a different site of yours. However, if all 3 sites have similar content, only different domain names and if you're doing this just to build more links or PR google will find out about it sooner or later
See Google do not know who's hand is covering what.. who is having how many websites.. it doesn't go to any hosting company for getting details about the domain or anything... whatever they know about websites.. they know from IP addresses.. ur CSS, HTML ect.. For knowing ur 3 websites.. it will check for ur IP address and if it will find ur class C IP similar it then it will tell that the websites are owned by a single authority.
Having sites interlinked from the same IP will impact on how good quality Google considers the links to be, however, it's not hugely detrimental by any means. Interlinking across 16 IP's or so on the same Dedi is a hugely effective method that i employ across a lot of my sites.