tedster - 8:27 pm on Oct 14, 2011 (gmt 0)
Essentially, bad neighborhoods are groups of sites (often pyramids or rings) that are used to artificially inflate backlink scores. The end goal may be webspam or something more malicious like malware distribution.
The sites in these bad neighborhoods often use the same template or theme. The bigger ones may use several different ones. The content is pretty useless and it exists only as a vehicle to put the links online, so you frequently see scraping and spinning to create the text that fills up the pages. The text from public domain sources is another tactic.
There are slightly mellower bad neighborhoods (also problematic) that are ways of sharing links with other sites who buy-in to the promise of increasing backlinks.
So it a site is "trading links" with others just because they seem to have good PR, then they are most often wading into a bad neighborhood.