I don't see that the format of a computer screen dictates which format a photographer chooses to shoot in, unless the computer screen is the final intended output for the image, and the image must fill the frame. In this thread is the assumption that computer monitors are what everyone is looking at photographs on, which just isn't the case. Books, galleries, magazines, newspapers etc. all haven't any issues exhibiting portrait-format. How the image is to be finally used is what dictates the format, and even then, cropping is always an option.
Computer screens rarely do an original image justice anyway. I kind of see online images as a cheap way to show people what you have done, but it doesn't show how well you have done it.
And a vertical photograph can indeed be viewed on widescreen monitor, it just doesn't fill the screen from edge to edge, which I don't see as a problem. What's wrong with negative space around the image as in viewing a print on the wall? As long as you are sitting in front of your screen and not more than a couple feet away, an image that is 900 or so pixels by 700 or so pixels is easily viewable. And anyway, monitors have never been portrait format - they've been 4:3 and now they're 16:9.