What do you guys do when you have to go use the restroom facilities? I tend to bring my laptop in with me since the loss of it would piss me off more than the embarrassment of taking it with me.
Plus, if others around me have seen me there long enough, I feel like they'll point out who/where the thief went when I come back out. You also just need to use your judgment. I'd never leave it there in an unfamiliar coffee shop or if I planned to be gone for more than 40 seconds.
Now, asking other people to watch it can be one more nice human interaction for the day if you feel the need.
Or, get a laptop with built in GPS and 3G internet, and hack the firmware to autoemail you the location on boot-up.