If you've ever used an iPad, you've no doubt seen dozens -- maybe hundreds -- of made-for-the-tablet ads, but you probably haven't seen one from Apple, unless you happened to glimpse a test in December for Disney's "Tron Legacy."

Well, now the iAd platform is officially open for business on the iPad, and Apple has its first paying customer: Unilever. That means app developers that have opted-in to iAd on their iPad apps will soon be getting checks from Apple.

Apple's iAd is far from developers only source of display ads: they can do direct deals with marketers or agencies or with ad networks like Millennium, Jumptap or Google's Admob, but iAd is integrated into Apple's OS, meaning they can check a box to opt-in. It also means marketers can traffic the same ad across all Apple devices.

The first ad to circulate on the platform is from Unilever's Men's Dove and pegged to the NCAA men's basketball tournament featuring videos from college greats such as Magic Johnson, John Thompson III and Bobby Hurley, teasing out the "comfortable in your own skin" tagline. Answer some trivia questions and you get a chance to meet Magic at a game in Los Angeles.

Why did it take Apple so long to get its iPad iAds in the marketplace? An OS update in November enabled iAds for the iPad, but it took months to get developers to adjust their apps to accommodate the various sizes of banners to drop in as planned.

Eric Litman, CEO of Medialets, says he's seen a significant shift since the first tablet ads appeared last fall, as agencies such as AKQA and Razorfish take over development work. "Six months ago we were building 100% of the ads on our platform. Now, the volume is up dramatically and we're building less than 30% today."