Turns out that there are a bunch of solutions for this available from the Apple iPad App Store, ranging from badly reviewed $0.99 apps to $30+ applications that are built atop the VNC (Virtual Network Client) protocol. I haven't seen the "Share Screen..." system that lets you share Mac screens back and forth, but perhaps that's coming in an update from Apple.

What I experimented with to see if I could get this to work is an app called Air Display, from Avatron software, a $9.99 app from the App Store.

Here's the link: Air Display [iTunes].

Download and buy it, then when you launch it on your iPad you'll find that there are some steps you need to do on your Mac computer to get things to work.

That should be no surprise, actually, since the two have to work hand-in-hand. Anyway, here's what the apps displays:

In a nutshell, go to avatron.com/ad and grab the installer. Run it...

When it's done, restart your Mac. Now along the top menu you'll see a new icon:

Choose the option to turn Air Display on and make sure that both your iPad and your Mac are on the same wifi network (a must for this to work) and you'll see it listed as an option:

You can open the Air Display Preferences if you'd like...

but you should also just be able to pick your iPad: in my case I'll pick "Dave's iPad", and suddenly my computer display restarts (screen goes blue for a second) and when it restarts, the iPad is running as a second display on the MacBook Pro! Awesome!

You can figure out your layout by going to Apple --> System Preferences... --> Displays and choosing Arrangement:

The blue box with the white line represents your MacBook (or iMac or other Mac) and should definitely remain the main screen. The smaller blue box is the iPad. Move it so that it's on the same side of the main display that you're going to put your iPad relative to your computer and you're good.

Turns out that running a second display over wifi is not as fast as a direct video monitor cable, so I have found that it's way too slow to run video or anything of that nature, and the resolution is pretty low too: it's 1024x768, but that turns out to be just dandy for things like iTunes, which is what I have running as I type in this article:

Very nice, and a cool addition to my iPad app library for sure.

Caveat Emptor: as I used Air Display in a variety of different settings I found that sometimes it'd connect without an issue and other times the Mac and the iPad just didnt' seem to see each other, even when on the same wifi network. Your experience may vary, but don't expect it to be 100% reliable and rock solid. More experimentation will hopefully help me characterize when it does or doesn't work, however.