a lot of sites use link/banner exchanging software/companies and this does not bother Google
That depends....
The following are examples of link schemes which can negatively impact a site's ranking in search results:
•Buying or selling links that pass PageRank. This includes exchanging money for links, or posts that contain links; exchanging goods or services for links; or sending someone a “free” product in exchange for them writing about it and including a link
•Excessive link exchanging ("Link to me and I'll link to you")
•Linking to web spammers or unrelated sites with the intent to manipulate PageRank
•Building partner pages exclusively for the sake of cross-linking
•Using automated programs or services to create links to your site
Here are a few common examples of unnatural links that violate Google's guidelines:
•Text advertisements that pass PageRank
•Links that are inserted into articles with little coherence, for example:
most people sleep at night. you can buy cheap blankets at shops. a blanket keeps you warm at night. you can also buy a wholesale heater. It produces more warmth and you can just turn it off in summer when you are going on france vacation.
•Low-quality directory or bookmark site links
•Links embedded in widgets that are distributed across various sites, for example:
Visitors to this page: 1,472
car insurance
•Widely distributed links in the footers of various sites
•Forum comments with optimized links in the post or signature, for example:
Thanks, that’s great info!
- Paul
paul’s pizza san diego pizza best pizza san diego
Note that PPC (pay-per-click) advertising links that don’t pass PageRank to the buyer of the ad do not violate Google's guidelines. You can prevent PageRank from passing in several ways, such as:
•Adding a rel="nofollow" attribute to the <a> tag
•Redirecting the links to an intermediate page that is blocked from search engines with a robots.txt file