Can you depend on Search Engine traffic?

Over on ipears.com the question of whether you can depend on SE traffic is raised and I think that if you are dealing with a niche blog, you almost have to.

I am definitely for not putting all your eggs into one basket so I understand the dilemma of having over 50% of your traffic coming from one search engine, however, in my experience, search engine traffic has clicked on adds at a rate almost 3 times that from direct links. Additionally I tend to get about twice as much traffic from search engines than what I do from direct links.

I try to get as many incoming links as possible which, in turn, generally give my higher SERPs, however, I can not ignore the fact that I get about 6 search engine conversions for every one coming from a direct link. If my stats are representative of what Jan sees, I say again that he almost has to depend on search engine traffic. I would just make sure that you rank well in at least two of the big three.