I've never left the gun unloaded, however I have twice forgotten to chamber a round
I use the same weapon my CCW/Nightstand/ETC. When its on the nightstand (When I use my glock) I often keep it without a round in the chamber.
Twice that I recall I've gone out either to work or run errands, and holstered it without chambering a round...realized it when I got home. Oops...