New Roomba-like household robots are popping every day, now. The Windoro consists of two scrubbing modules, one on each side of the glass, held together with magnets:
The robot uses distance sensors, attitude adjustment, and obstacle detection while doing its little window waltz, employing detergent and a series of spinning pads to wash up as it goes.
This robot was developed by the Pohang Institute of Intelligent Robotics in South Korea. You can watch a video of the robot in action at the link.
Link via DVICE | Photo: DVICE
At first I thought it might be practical for high rises but it will need people to move it between windows wherever there is a gap, break in the glass or other obstacle. That, or buy thousands of them for every window. I wouldn't buy a robot and hire two people to watch it clean one window in the amount of time it takes one person to clean about ten windows himself.
I don't know if I want a cleaning robot with an attitude that needs adjusting. (o_0)