I agree as well. When I'm in others's churches, I do whatever I feel as long as it is not offensive (like knocking over the altar table and ripping up the bibles or something.) When I bring friends to my church, I tell them they can do as little or as much as they feel comfortable with. Some cross themselves, even the Protestants! Some venerate the icons. Some just stand next to me and look bewildered. It's no biggie.
Much of the time, however, I do not cross myself in other's churches. Usually because, for me at least, it doesn't feel like church, and it almost never feels like a time when one should cross onesself. It's the way it goes, I suppose.