Is this against google's webmaster guidelines?

I was trying to learn from a top ranking site and after a thorough checking I found lots of high PR backlinks(mainly PR 3 or 4), and these sites only have several pages, 10 at most, so basically they are only used for backlinks. My guess is these sites were bought immediately after they are expired with good PR values, and to my surprise a lot of these sites still have powerful backlinks from other high PR websites whose owners obviously have no idea the ownership/content of the site they are linking to has been changed.

From what I saw, some 400 words articles have more than 10 links to totally different niche-sites, and most of these articles make NO sense at all. These kind of backlinks must have passed very good link juice, as the site they want to promote ranked high for very competitive keywords.

So I think those nonsense articles obviously are against google's webmaster guidelines, but I do noticed there's also some carefully written articles which read pretty well and links to different niche-sites, will this also piss off Big G?

Well I'm actually considering building my own link networks, so please give some suggestions. Thanks