The truth is, your desktop is becoming more and more irrelevant. Ask yourself this question: How many of the programs you use on a daily basis are online instead of running off your desktop? Adobe has announced that they plan to release a web-based version of Photoshop in the next 6 months. This is a huge deal, not only because such a major software is making the move, but because of the business model behind it.
According to an article from CNET, "the hosted Photoshop service is set to be free and marketed as an entry-level version of Adobe's more sophisticated image-editing tools, including Photoshop and Photoshop Elements. Chizen envisions revenue from the Photoshop service coming from online advertising."
In the next year or so, we're likely to see others follow-suit, particularly if the business model pays off. That is wholly dependent on how the ads are integrated into the offering, and if consumers find them worth the trade-off for the price.