Yeah, that's why I'd probably ask someone to keep an eye on it, rather than take it with me - I often do that with possessions, although not a laptop, in public situations (cafe, bar, train, etc.) I'd rather live in a society in which we trust each other to keep an eye on our stuff, than one in which we have to take everything with us for a quick pop to the bathroom. Of course, I'd rather one in which the threat of something being stolen didn't exist at all ...