The Google+ mobile app is available for the Apple iPhone 4 now. Here's a trick to make it work on your iPad, too.
Note: I used the iPhone Configuration Utility for this piece. While that utility is available for PC and Mac platforms, I found these steps only worked on the Mac.
If you haven't yet, open iTunes. Download the Google+ mobile app for iPhone from the iTunes App Store. It's free.
Next, download and install the iPhone Configuration Utility for Mac from Apple’s website.
Installation is easy. Make sure to follow the wizard and accept the defaults.
Next, open Utilities and launch the iPhone Configuration Utility.
Highlight Applications and click Add. Then navigate to User >> Music >> iTunes >> iTunes Media >> Mobile Applications >> Google+ 1.01.ipa and click Open.
You'll see the following screen.
Now plug your iPad into your Mac. After a moment, you'll see it listed under Devices.
Highlight iPad. Click on the Applications tab. Scroll down until you see the Google+ mobile app. Hit Install.
It just takes a few seconds to install. Eject your iPad and unplug it. You'll see the icon for Google+ on your Home Screen. Just tap it to launch the application.
That's all there is to it. Sign into your Google+ account and you'll be able to get it on the iPad.
Of course, it's not optimized for the iPad's screen resolution. So run it in 2x mode.
While you're waiting for an official iPad Google+ mobile app, this workaround will let you make use of Google's iPhone app for now.