Vimov, the developer of Weather HD for iPad, published an estimate of App Store sales based on the volumes of its own top ten iPad app, this concluded that Apple is selling over $372,000 in iPad apps-per-day and will hit $1 billion in annual sales in two years.
The company's $1 Weather HD title was among the first iPad-specific apps available in iTunes. It managed to sell nearly 2000 copies before iPad even became available, placing fourth in iTunes' Top Selling list behind Apple's own Pages, Numbers and Keynote.
Vimov suggests iPad apps could hit a billion dollars in in sales per year within two years. Separating iPad app sales from iPhone apps is somewhat difficult, supplying unique optimized interfaces for each. For users of both iPhone and iPads, upgrades of such apps won't count as either downloads or new sales, because Apple does not count app updates as a new app download.