Also Link Popularity reflects your effort to boost your traffic. Its easy to search in a search engine all pages that Link to your web page from outside your site.
Hereby you can see in which search engines you can have good link popularity and in witch engines not. When you see for example you have a lack of links in Teoma and know you score well in MSN, you can put effort in getting more Inbound Links in Teoma.
Tip: in your SEO Effect is also a link popularity included. As with the rank reports you can see your link popularity over time and for different engines.