Screen real-estate is a lot like money, there’s really no such thing as too much. So if you’ve every gazed at the screen of your iPad and thought, “it would be so awesome if I could use this thing as a secondary monitor,” you’re not alone.

The good folks over at Avatron have, in fact, been secretly reading your mind via Wi-Fi, and have come up with a brilliant solution: their Air Display app.

In truth, it’s more than an app. It’s the combination of an app that runs on your i-device and program that you install on your PC or Mac that runs invisibly in the background. The magic happens in the communication between these two chunks of code, over your home Wi-Fi network.

When everything is setup and configured correctly, you can extend your desktop onto the target device with a couple of clicks. As long as your gadget is running the Air Display app – zap – there’s your background wallpaper from your computer magically rendering itself on your iPad, iPhone, etc.

If this was all that Air Display could do, it would be worth the price of admission right there. But wait – as I wade dangerously into infomerical territory – there’s more…

Air Display automatically recognizes the orientation of your secondary display and rotates the contents of the screen to match. You can also – via the server software on your computer – designate where in space, relative to your primary monitor, you’ve placed the iPad. If you’ve ever used dual (or multi-) monitor mode in Windows or in Mac OS, this will be completely intuitive for you.

Finally, and possibly the coolest part of the whole package, you can actually interact with the content being displayed on the i-device. Browser window? You can scroll and click with your finger. Calculator? Tap those number buttons. Painting program? Paint away my friend.

The first time you try it out, you’ll get that same giddy feeling you probably got the first time you surfed the web on your laptop via Wi-Fi without a single cord restricting your movements. It’s really that great. At least, it is when it works. Keep in mind there are several things that can influence the performance of Air Display, such as the number of apps running in the background of either your i-device or your computer, the network activity on your Wi-Fi network and other factors.

If there’s one thing I’d change about Air Display – and this is going to sound a little silly given the app’s name – I’d like the option to connect my device via the USB cable for a truly bullet-proof experience. I don’t know if this is even possible within the limitations of the iOS SDK, but it would be a welcome upgrade.

So if there’s an iPad owner on your holiday gift list this season and you’re looking for an inexpensive gift that will elicit a disproportionately large amount of gratitude, I humbly suggest Air Display. It should fit the bill nicely.

On a somewhat related note, readers, do you find app reviews like this one valuable or not? We’re thinking of making it a regular feature here on Sync, but not if you think it’s a waste of pixels. Please take our poll below, or just leave us a comment.

If you’re an app developer and you think your work is so ridiculously awesome that the whole world (or at least the Canadian part) should know about it, drop us a line and we’ll be sure to check it out.