I'm having fun with my new iPad and thought you might enjoy a quick tutorial on creating iPad wallpapers in Adobe Illustrator! I have so many repeat patterns locked in my art vault and wouldn't you know, they make a nice background for my ever-growing collection of apps. The art licensing business dictates that you have lots of art and patterns on hand, and many of them go unused so here's a chance to give some of your art a fun new purpose.

The basics are quite simple, you start with a square that is 1024 x1024 pixels. The square format allows for the vertical to horizontal rotation of the iPad. Repeat pattern designs are a great match for iPad wallpapers, because they are designed to work perfectly well in any format, regardless of how it's cropped.
In Illustrator, set up a new document (File > New...) with units set to pixels and the dimensions set to 1024 x 1024 px. Set the color mode to RGB and the Raster Effects setting to 72 ppi.

Next, make a safe area guide to visualize the part of your artwork that will be cropped as the iPad rotates. Start by creating a square at 768 px. Center the square on your artboard using the Illustrator Alignment icons at the top control bar. (For more info, see the bottom of this earlier post.)
Select the square and choose View > Guides > Make Guides to turn the square into a guide. You'll be able to see the guide as you work, and it won't show up in your exported image.

Create a new layer named "safe area guide" and move the guide to the new layer so you can lock it and keep it separate from your artwork. Save your new document. (Also, save it as a template for future iPad Illustrator Wallpaper designs: File > Save as Template...)

Now copy your pattern art from another file and paste it into the new document. The area inside the square guide will be visible in both the horizontal and vertical orientation. If you are creating the wallpaper for distribution, you'll want your signature or copyright to appear inside the safe area, so it remains visible.
When you are finished tweaking your art, choose File > Save for Web & Devices. Make sure to check Clip to Artboard to crop your art to the 1024 px square. Preview and choose the file type that works best for your art, jpg or png.
For more information, check out this post on Digital Citizen. This is where I found the safe area dimensions and the post goes into more detail about which areas of your wallpaper are visible as the iPad rotates.
My current iPad wallpaper is set to one of my favorite unsold designs: Club Penguin by Laura Coyle Download Coyle-clubpenguin.png, it's free for your personal use. It reminds me of a pattern you would see on a pair of flannel pajamas for the winter, just right for cozying up and working in Illustrator!