Colour calibration is an important step in image editing. You do not need it for all edits, only for edits that change colours. You do need colour calibration to see if colours need changing.
Datacolor make the Spyder3 in three versions, the cheap Express for a single monitor, the Pro with more features and for multiple monitors, then the Express for full time professionals managing many types of equipment. The Elite is just a software change from the Pro and the software is available as an upgrade, which means you can buy a Pro then upgrade to an Elite.
The price in Australia varied from AU$219 up to AU$388 during June 2010. The cheapest price, when I purchased mine, was at Jerry Gibbs Camerahouse in Perth. The cheapest price in Brisbane, Melbourne, and Sydney for a Spyder3 Pro with the manufacturers Australian warranty was at Digital Camera Warehouse.
You plug the device into a USB port then install the supplied software. The software with mine was so out of date, it was unusable and should be labelled a beta version. I had to immediately download an updated version, which worked but required registration and my email address. Hopefully one day someone will provide this type of hardware with free open source software with no license restrictions or registration rubbish.
The software requires one manual calibration then can automatically change the calibration if the light changes. After the initial calibration, the Spyder3 sits on your desktop reading the light level in your room and major changes will make the Spyder3 software recalibrate. My monitor is used with sunlight during the day and requires three or four recalibrations during the day as the light changes. You have to recalibrate while logged in as an administrator or set the software to run as a service to allow automatic recalibration.
Recalibration is of most use when your monitor can display colour accurately. My Asus monitor changed a little bit during the initial calibration and the change was worth the effort. The result is still not good enough for fine tuning colour. A similar size monitor with accurate colour would cost five times as much and would require changes to my office to reduce colour reflections. I would also have to close the blind to limit the influence of sunlight.
Many image edits are only to change size and do not alter colour. You do not need colour calibration when you create content from images and only alter the image size or create thumbnails.
Photographers can work without monitor calibration if they carry colour reference cards and use them during photography. At the start and end of each shooting sequence, you include a colour card, or a white, grey, and black reference. You use software to adjust the first image so the white is white, the black is black, and the grey is grey. Your software should then apply the same change to all other pictures in the same sequence. You should not need colour changes after that.
Check the last photograph in the sequence to ensure the colours are correct. If the white, grey, or black is wrong, the light changed during the shooting sequence and your colour adjustments are not accurate for the final shots of the sequence. You will have to split the sequence where the light changed and adjust the last shots based on the colour references in the final shot.
Does someone have a colour standard you have to meet? Corporate logos and team uniforms have specific colours. When you photograph those types of items, check the specifications for their colours. You can use their RGB and HTML colour specifications to set up comparisons. The calibration of your monitor does not matter so long as the colours in your images match the colours in the references.
Calibration is most useful when you do not have a reference image and have to match a colour in your image to something not on screen. You want your monitor to accurately display the colour the way most people see the colour. Calibration becomes more important when you have to match an on screen colour to the way it will print. No member of the public will see the colour exactly the way you see it and every printer produces different colours. You make your colours a little bit more accurate by buying a good monitor, then a little bit more accurate by calibrating your monitor, then you use a professional calibrated printer, then you run test prints.
Monitors with accurate colours
CRT monitors produce colour more accurately than LCD monitors. LCD monitors cost twice as much to get similar accuracy. NEC and Esio product LCD monitors with accurate colours. The NEC equivalent of my AU$500 Asus is AU$3000. The Esio equivalent is AU$4000. There appears to be no technical difference between the two as far as colour goes. The Esio recommends a specific expensive colour calibration unit for colour calibration. When you spend $4000 to get a monitor with accurate colour, spending $500 or $600 on a calibration unit is ok. The Spyder3 is for everyone else.
Automatic light level adjustment
Some LCD monitors automatically adjust their backlight intensity to adjust for changes in light level. The Spyder3 adds that feature for all monitors. The automatic adjustments in monitors and the Spyder3 do not cover changes in the colour of the light. When the sunlight changes to red during sunset, your monitor representation of colour is useless because your eyes are swamped by red. When you switch from daylight to artificial lighting at night, you should recalibrate for the different colours in artificial light.
If you select the right tubes to use in your lights, your artificial lighting will be closer to daylight but never completely accurate. Some image editors leave their blinds shut all day and work only in artificial light so they can reduce the adjustments to their monitors.
The eyes have it
Your eyes adjust for colour in all sorts of strange ways. Sugar and caffeine are two of the chemicals that can temporarily change the sensitivity of your eyes. Wear dark grey or black clothing because the colour in your clothing can reflect into your eyes. If your image contains a strong area of one colour, that can change your perception of that colour in relation to the other colours in the image.
Every so often, look at something different and neutral for several minutes then look back to your monitor to see if your perception of colour is still the same. Perform the same test when calibrating the colours on your monitor.
Monitor colour calibration is a good idea for monitors under AU$1000 and compulsory when you invest several thousand for a monitor with accurate colour display. The Spyder3 Pro is a great start for colour calibration.