I started this thread from my own experienced 7 days ago before jumped into this conclusion. Here is my story. I have my real estate site, ranked top 3 in Google.com for niche competitive search term with PR5 with year old ages. Then I had launched new real estate blog on the same ip (I am using reseller host and all of them have same ip) and linked from homepage to them. 2 days after, all of them suddenly disappeared from allintitle and allinanchor search operator results. plus my main real estate site ranking down a little. I took the link off and my ranking back after a day passed. I moved my main real estate site to another host with different class C ip and linked to them from homepage again. I checked all DC's and found sites ranking had been downed to 430 in many DC's!! From 3 to 430 !! I suspect this is a cause then I took the link off again and my rank has back all DC's with in a day after took the link off. Here is my conclusion. If your site has authoritive from Google, from my perspective, the site ranked top 10 in competitive search term or have high PR with old ages, must not linked to new site. Especially if they are sandboxed. new site homepage ----> new site = fine new site homepage ----> authoritive site = better authoritive site homepage ----> authoritive/old site = Better authoritive site homepage ----> new site not sandboxed = worse authoritive site homepage ----> new site with sandboxed = worst/hard penalized you will get This rule apply for subdomain under current site too, I created new article directory under subdomain of my main real estate site then linked from main site and got same penalized. In my opinion, Google try to put site that sell their homepage links on high PR page down to prevent sell links spam. They need old site linked to good sites as good reference, not new site with a much less content/value for visitors. If you still want to do, just make sure your new site hosted in a different class C ip before linked from old to new one. Don't do fault like mine. I think Google has recorded my new real estate site as red flag if they got link from my old real estate sites, even different class C ip because they had detected all of them had same class C ip when the first time they crawled. How to determine sandboxed? who knows exactly, but I always checked site ages and their link popularity and sites before linked from my homepage. In my opinion again, I think this rule has not apply to links from directory/sub category/subpage but apply to high PR homepage only. If your site ranking down like a rock with unknown reasons, check who you linked to on your homepage first. Good luck with your site.