As a US national I passed through German security on the way to India in 2005-ish, and they did the same - turned on my (work) laptop, bade me log in, and carried it into a back room for around 20 minutes where they did... presumably something. It seemed relatively routine to the officer, though in retrospect perhaps she twigged me for something and was just acting nonchalant. I guess EU members don't have to deal with German customs? Or has this been tightened up in the interim? By coincidence I've only gone through Dubai since.