For myself this was something that varied depending on subject area and or author. I'd guess under 1% because I use to use google heavily for hours a day. Of that 1% or less, new topic interests or research of course accounted for a bit more than half in my estimate, the rest over my time on the web while using google, much of those sort of searches is due to written works by what I refer to as Fluff Bunnies - the journalists or article author who turned an informative paragraph into two pages of fluff full of whatever strange new terms and expressions fills the pages - when it's a field that I'm fairly confident in but have never heard such terms before.
Last two or three years I use DDG predominantly and only use google for quick texty description stuff attached to youtub link ... searcher give very little these days, but still do just in case.
