cgrantski - 12:19 pm on May 19, 2009 (gmt 0)

It's probably not bookmarking. I mean, do people really use bookmarking all that much these days? Not enough to account for this, I don't think.

It's probably just other sites, usually shopping aggregation search sites, that display a link to your product page. If the link is an ordinary javascript link that opens your site in a new browser window, then there will be no referrer for anybody using IE browsers.

A lot of the shopping sites open new windows this way, because it's in their best interest to keep their site open in your browser.

One way to get support for this theory is to run a report just for Firefox and Safari users. If the proportion of those referrer-less internal-page-entry visits drops dramatically for these two browsers, it fits.

Your situation underscores the necessity of having all possible links to your site (through affiliates, banners, pay per click) marked for tracking with a parameter in the link URL. Relying on the referrer is no good any more. Even for search. On sites I track, 9% of all pay per click traffic has no referrer because of the link behaviors of various affiliate search engines --- it's a much higher percentage for Content Network PPC.