Say there's a PR5 blog where you can comment and you leave two separate comments with two links to two different sites of yours that are hosted on the same account. Would that not be considered as good, if they have the same IP? Or should I create different hosting accounts for these two?
The IP of the site that is linking out is more important than the IP of the site receiving a link. You're fine, but don't be excessive with it.
I believe that the important thing to consider when link-building to rank higher in search engines is to remember that its got to create a vicious cycle. You need to build backlinks to your site from sites/pages with relevant content. Yes, unique IP is best. But not only is that a long process but it can get expensive if you're buying backlinks from individual sites. To rank higher in search engines we cannot forget that we must build backlinks from unique IPs but also build links that WILL attract natural visitors. This in turn will help your site naturally rank higher and higher in Google and others. Placing your link in different areas of the same IP is not all bad if you see things that way. For example, posting your link in different blog-posts in the same blog. If you publish 10 unique posts in a blog or article site, the PR juice will not be as good, but if each post attracts say 10 visitors to your site - then that's 100 new visitors who crawl your site. Google will pick up on the fact that your site is getting more popular with ACTUAL visitors and rank you higher. So don't just concentrate on unique IP. Hope I helped
Yes, Mass linking will effect your ranking and you can put into google sandbox after which your popularity will totaly nill as well your pr will not increase from 1..... Becarefull