I got blasted by my saltwater rig once when a heater had broken. Reached into the sump to readjust a pump -- and let me tell you, I didn't need a second attempt to know I was getting shocked. Of course, saltwater is a much better conductor than soft water.
After that I went with a titanium heater on that tank.
Would rate the experience as not fun, but no lasting damage. Wasn't quite as painful as when I took 110 across my body rewiring an outlet for which I was "certain" I had turned off the breaker. Now I check with a small lamp.