Forum Moderators: not2easy
There are some pretty good studies around page layout and the correlation between element position & hit frequency - the adsense program supplies some nice diagrams that might help - have a rummage in their help pages.
Other searches for you might include a fairly recent study into eye movement over a web page - i think it's called eye tracker.
From a personal point of view - I tend to place the search box top right inside a nice graphic. I figure it should be prominent and available to use one every page of the site - intrinsic to navigation, as it were.
As standards like this develop, albeit pseudo, it tends to educate users to look there and if they don't find it they get confused.
Regards,
Ric