I used to exchange links with other webmasters using LinkMarket and Link2me... what happen?
My site appeared in link farms, my links was deleted by 30-40% webmasters right after deal... I got bunch cheap links. Moreover, many sites i added on my pages dissapeared later and later people bought domain names to host Adult sites, casinos, illegal sites. So, i was linking really bad sites. One day i deleted all links (about 800) i hosted from Link2me and LinkMarket.... week later my Google positions increased without any promotion!
Also, spending my time and money (for link exchange servise) i never got any pr4 or highter links...
As example i can show you link farm i picked for my site:
http://www.evolvelb.com/partners.php...4a313b5929f3e/
http://www.evolvelb.com/partners.php...874fae3a0a6cc/
http://www.evolvelb.com/partners.php...fb0bc352c9cae/
...... and so on... more than 1000 pages!!! 100% link farm. Today i afraid that one day Google will discover this and ban my website.