On two of my site I notice a 40-60 traffic ratio. 60% being search traffic. I think if your site gets very less direct traffic, Google will send you less search traffic.
One site hit badly by Penguin, one site isn't affected with Penguin.
Before Penguin, the ratio of traffic was around 85-15 I think.
If people aren't bookmarking your site, not coming to your site directly, it means your site doesn't have compelling content, so your site doesn't deserve much search traffic.
Anyone else seeing this trend?