>Have any of you seen studies with percentages on where most "buyers" come from in terms of engines & directories?
As luck would have it, I had this very question a few years ago. In July, 1998, I took the logs from my 5 major clients to find this out. I used sales I could actually track (i.e., those who bought on a trip directly trackable from search engines). Keep in mind, though, that not all consumers buy upon their discovery of the site. Presumably, many comparison shop and come back. Those are not counted in this study.
Between January 1, 1998 and June 30, 1998, there were 1,665 sales which fit that criterion.
stamp collecting site (821 sales)
gifts and collectibles (646 sales)
software reseller (127 sales)
computer hardware (54 sales)
shotcrete (17 sales)
Because of the vast changes in search engines as well as ecommerce in general, I doubt that these have pinpoint relevancy, but it is a place to start.