Demographic data in Analytics

I know I know, comparing data from different sources will give me different results, but what if the values of my report are binary: 0 or 1, yes or no, new or return visitor, female or male? In this case I don’ care as much about the absolute occurrences of Zeroes and Ones, but rather the proportion between the two values. I will then optimize for the value that gets > 50%. So if I somehow knew the gender mix on my site I could change the color scheme? Sounds like a decent optimization idea, right?

Well, I looked at two recent/updated sources of demographic data: Google Ad Planner (via Jeff) and Yahoo! Web Analytics (via Dennis) and compared data from the same site, an established multimillion dollar online retailer.

From Ad Planner:

Picture 97

From YWA:

Ywademographic  

What I don’t understand is why one tool says there are mainly men visiting the site whereas the other says just the opposite. Granted, the way the data is computed is undoubtedly different, but I am still left with the decision: do I optimize for one or the other?

Or are they both right? Perhaps I should optimize my site based on the source of the traffic: traffic from Google gets stylesheet A and traffic from Yahoo! properties gets stylesheet B.

Has anyone had luck in doing onsite personalization based on demographics, or are demographics best used in ad campaigns?