Fabian Kreiser has recently updated his screen capturing app for Mac OS X to include support iPad screen captures. Like previous iterations of the app, version 1.2 of iPhone Screentaker allows you to add certain design elements to your iPad screenshots. These include encasing them an iPad and setting the orientation background color. Images can then be saved as either JPG or PNG, with the option to scale to fit iTunes.
One little quirk about the app is the "Capture Screenshot" button. While its existence would seemingly indicate an associated action, in my experience clicking on it didn't do anything. I wasn't able to find anything documenting its function, either.
Screen capturing has been a feature on the iPhone since iPhone OS 2.0, and taking a screen capture is as simple as pressing down the sleep and home button at the same time. The feature serves a myriad of purposes, from facilitating the marketing of an app and documentation workflow for developers, and for allowing reviewers, like us here at TUAW, to highlight certain features of an app.
iPhone Screentaker is available as a free download at Fabian Kreiser's site.