You have two thing to consider here...
The computer (and screen) that people will be looking with - and the browser that's being used.
If you are posting images online for photographers & graphic designers using a calibrated screen can be an advantage - as the odds of your client looking with one is quite good.
If the images being posted are for general public, the odds are their screens will look exactly like they were as they came out of the box.
In that situation you have to just guess. Assume the computer has a LCD screen which will be too bright and too cold (by photographers standards) which means if you've uploaded an image that has been colour corrected on a profiled monitor it will be light and blue.
If you look at a file on a profiled monitor that has been adjusted on a screen that has not been calibrated, the image will be too dark and yellow.
As vitually no browsers are profile aware (Safari is the only one as far as I know) you would be best to only upload sRGB files.