For the most part they're images created in a program like Adobe Illustrator, then converted to gif or jpg and placed on the site via CSS. In some of them, the images are used as cels in Flash. The web technology aspect is (for the most part) not especially complicated; the point is to draw attention to the use of illustration as a design element.
One exception to the above is http://www.volll.com, which has some nifty JavaScript animations.
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For the most part they're images created in a program like Adobe Illustrator, then converted to gif or jpg and placed on the site via CSS. In some of them, the images are used as cels in Flash. The web technology aspect is (for the most part) not especially complicated; the point is to draw attention to the use of illustration as a design element.
One exception to the above is http://www.volll.com, which has some nifty JavaScript animations.
Edit: sorry, cross-posted with you.