According to Neiljhonson in a forum, 60 to 70% traffic from search engine is good but along with traffic you should track bounce rate of your visitors – how much time they are spending on the website and which is the most attractive page in your website.
http://forums.digitalpoint.com/showthread.php?t=1431861
Diversifying your SEO is vital considering the possibility that your main site could be banned in major search engines like Google. An SEO Monopoly can help you form multiple sites in your niche that attract your potential customers.
