I take a 10" netbook in a sleeve, a kindle in a case, and an ipod and headphones in a padded TB pouch with me when I travel. I put them all in a packing cube and I have attempted to leave this packing cube in my luggage when I go through security.
Two out of the last three times I traveled I was asked to please remove the packing cube, because it was too "dense" and they couldn't tell what it was through the xray machine.
Last time I took out the netbook and kindle and put them in a bin to go through the xray.
Just FYI - if you are packing electronics and want to leave them in your luggage, spread them around a bit so they don't look dense to the screener. Next time I think I'll leave the netbook in the luggage and put the kindle and ipod in my purse.