There are many tools to analyze site popularity trend. You probably use Alexa, Compete, Google trends, quantcast and maybe others. But have you tried using del.icio.us ?
When you visit a site url page in del.icio.us (for example http://del.icio.us/url?url=www.google.com)
You can see who bookmarked google.com and when. Analyzing how many people bookmarked a site each month can tell us a lot on site popularity growth or decline. I created this simple tool so you could check your favorite site popularity trend according to del.icio.us’ huge community. I hope you enjoy it 
