They are very useful! However, I would say to be careful before making a decision on which products you buy. I usually stay away from any companies that make products that haven't been tested or don't publish their test results, because they may actually NOT be very useful!
Check out the new IsoAcoustics stands. They have had a lot of people talking recently and they published some great test results. However, if you don't have any acoustic treatment & bass traps in your room I would focus on that before isolation pads / stands - acoustic treatment will make a much larger difference in the room sound than monitor isolators.
Also helpful to know, are your speakers on your desk or on stands?