I used the Copic Airbrush System to create the background for this Halloween card.  It is a fun technique, but be warned that your Copic marker needs to be quite juicy for this technique to work well, and this process can use up the ink rather quickly-- especially if you create a lot of large backgrounds.  If you should decide to invest in this system, I would advise that you also purchase the ink refills for the markers you plan to use most often for the airbrush system as there is nothing more disappointing than running out of ink in the middle of a project!
Picture
The Copic Airbrush System can be powered by canned air or a small compressor, but if you plan on using this technique a lot, a small compressor would be a worthwhile and cost-effective purchase as the canned air really doesn't go that far.

A few other tips to keep mind:  Make sure your work surface is adequately protected when using the Copic Air System as depending on how far from the surface you hold hold the airbrush gun, there will be a certain amount of overspray--which can include your fingers if you are holding down the cardstock!  And although the fumes are not overly noticeable, you should still work in a well-ventilated area.

There are a lot of great tutortials and reviews available on this subject on the internet, and I would advise checking some of these out and doing some research before making a final decision on whether or not to purchase this item.  Or just visit the Copic Website at:

http://www.copicmarker.com/products/airbrush-system/