What good does a color calibrated monitor do if no one else has one?
You calibrate a monitor for yourself so that you will see the colours in the digital file accurately displayed on the monitor.
If someone else wants to view your files on their monitor and it isn't properly calibrated, they won't see the colour from the image correctly, and that's their fault. Look after your own monitor properly for your own reasons (expansion below may be almost hidden).
There is more to monitor management than just calibration however.
No matter how well a monitor is calibrated it will still not be able to display as wide a range of tones (forget about colour here) as can be recorded in a digital image file, and it is up to you to compensate for this. A digital image can represent up to 256 tones, ranging from 0 up to 255 (which can be read off in the Info Palette, which I strongly recommend you to have open at all times, and to refer to it continually). Your monitor CANNOT display all of these tones. Monitors differ slightly, but the range is usually from about 20 to 250. You won't go far wrong if you just adopt these figures, although it is not at all difficult to determine the precise characteristics of your own monitor. Taking the given figures, it means that, at the darker end of the range all tones from 0 to 19 in the image file will appear the same tone, basically BLACK on the monitor. Similarly, all image file tones from 251 to 255 will be undistinguishable from WHITE. This is clearly undesirable and the aim should be to adjust the tones in the image file so that the very darkest are re-rendered to value 20, and the very lightest (excluding specular reflections) to value 250. This can be done using a RAW file, or in Photoshop, by placing colour pickers at both the darkest and lightest points of the image and then using Curves to reset the values of those points to 20 and 250 respectively. The procedure will not only achieve the stated aim of avoiding large areas of full black and full white, but will also ensure that the full range of available monitor tones will be covered.
I will not go any further into the precise details and further ramifications of the above procedure, but I would be willing to do so if anyone is genuinely interested.
GHK