This is simply my personal observation of my experiences in using the i1Display2 and Spyder3 monitor calibration tools very recently.
Together with my 15" and 17" Mac laptops I recently purchased a second hand Mac Pro (2.66 Quad). I upped the Ram to 12Gb and replaced the two rather weak NVidia 1200GT cards with an Ati HD 3870 card (512Mb) running two HP LP2475w 24" monitors.
Before upgrading the graphics card I was unable to calibrate both monitors to produce the same colours within any image. One was weaker/darker than the other. I was using the i1Display2 on 'Easy' mode (as per Scott Kelby's recommendation in his books) - having tried the same on 'Advanced' mode without success, having spent a long time trying, and blowing my mind in the effort. It seemed that the problem was getting the white balance on both monitors to produce the same output.
Last week I upgraded my printer to the Epson 3880 from my Epson R2400 and with the relative shortage of ICC profiles from other paper manufacturers (come on Ilford - hurry up) I took the plunge and bought the Spyder3Studio SR kit - primarily for the print calibrator. Using the Spyder3 Elite, part of the pack, I attempted to recalibrate the two monitors - the result was the same re the white balance.
Nearly there folks!
Feeling somewhat fed up I happened to re-watch Michael Reichman's video no.4 from 'Camera to Print' and right at the very end (so close to the end that I missed it first time around), having shown how to use the i1 unit, introduced me to a piece of software that
he uses rather than the i1 software - ColourEyes Display Pro (
www.integrated-color.com). He rates it as 'highly recommended' as it contains masses of information and help files. "Well" I thought "if its good enough for him ...." and downloaded the 10 day trial version. It works with many of the commonly available devices including the i1Display2 and the Spyder3. It guides you through the process and after a mere 5 adjustments on the left monitor, and 4 on the right one, I had a 100% accurate white balance on both. Now I am a very happy teddybear - confident in the fact that the same image on both monitors will look the same when I use them in LR 2.5 or Photoshop CS4. Integrated-Color are presumable happy as they have a new customer and several more dollars as a result of my purchase of the licence.
I am convinced of the necessity of monitor calibration as a bare minimum in being able to faithfully reproduce what you see on screen. My advice, no matter which monitor calibration device you have, would be to try the 10 day fully-featured demo version of the software - it works!
By the way I have no affiliation to 'integrated-color' whatsoever - I'm a UK cop with only six months to go before retiring after 30 years toil.
