Ditto to Tom ... I work most days of the week in a cafe and have never experienced even a shred of worry or a hint of threat. Because I go to the same cafe repeatedly, I know the staff keep their eye on my stuff, and I don't have a second thought leaving a Mac Powerbook, cell phone, notebook, and Mt. Blanc pen, to venture upstairs to the toilet. I do tip well, but regardless, it is clear they protect my stuff. Become a regular, tip adequately, and don't worry about it.
Another ditto to the high level of paranoia exhibited among expat here. This is hardly different from any big city anywhere in the world, a few are worse, a few are better, but most are pretty much the same.