Adobe's decision not to upgrade the current versions of its applications for Vista makes it the most visible software maker to struggle with the incompatibilities created by Microsoft's new operating system. But it's hardly the only one. The one I'll miss the most: Wallnote, a nice little Web-based note-taking app that's dying along with Active Desktop.I know, Active Desktop isn't the best idea ever to become a Windows feature (possibly because it may be one of the least usable). But Wallnote makes it work. It puts two columns of text on your desktop, one for text notes, one for to-do items. You could cut and paste text from a Web page, capture a URL, throw a reminder on the to-do list. It does something simple, but it does it well -- at least until its creator takes the server down in May.

I got an e-mail last week from Wallnote's creator, Alex Griffioen. Wallnote's time has come. Why? Because Microsoft has pulled the plug on Active Desktop. There's nothing like it in Windows Vista.

Vista is a challenge to commercial application developers for a couple of reasons. Because it's so different from Windows XP structurally, for one thing. The completely different graphics architecture of Vista has imposed a major burden. One company president who makes video hardware told me that his developers spent the past year trying to rewrite the software viewer shipped with their products to meet the still-moving target of Vista.

The other thing is that Microsoft has been less concerned with the backward compatibility of Vista than it was any previous version of Windows -- both of hardware and software. Remember the "Windows compatibility settings" for older applications in previous versons of Windows? There's nothing like that in Vista.

This combination is clearly what's driving Adobe's decision. Like my friend the hardware guy, Adobe knows the work required to make its applications compatible with Vista is huge, and the costs are high. And it's decided it has to pass those costs on to its customers. The primary result for Adobe customers will doubtless be delay -- they'll delay spending the money to upgrade their Adobe applications as long as they can, and that means they'll delay moving to Vista in order to run their existing versions of Photoshop and InDesign and Macromedia Studio and the rest. Adobe can tough it out. Vista will put a double whammy on its revenue for the next couple of years -- the cost of developing Vista-compatible versions and the sales hit of not being able to sell less expensive upgrades to users who will avoid shelling out for Vista-compatible versions for as long as they can.

Wallnote won't take that much of a revenue hit -- it's free, after all. And Alex Griffioen's problems with Vista aren't the same as Adobe's. His app isn't broken in Vista like Adobe's are, but it works better with Active Desktop: The premise of its usefulness was that it was always available on your desktop, and Vista doesn't make that possible. (Griffioen isn't alone. Corporate developers use Active Desktop to display Web content like SharePoint pages, and they're looking for alternatives, too.)

Griffioen is determined to keep going. He's already got something new and improved. He calls it Nutshell. It's got the familiar quick notes and to-dos, and it adds a nifty search box that lets you pick the service you want to search and enter a couple of characters to identify it: "wp Active Desktop," for example, would search Wikipedia for Active Desktop, and "gi trackball" would search Google Images for pictures of trackballs. There's a long list of built-in abbreviations, and the best thing about Nutshell is that you can extend it by adding your own search domains. I've added InformationWeek.com and TechEncyclopedia searches so I can enter "iw Adobe" or "te TLA" in Nutshell, for example. Another neat new wrinkle in Nutshell: you can distribute your notes and to-do lists as RSS feeds. And that gives Griffioen a way to get back on the Vista desktop, sort of. Vista users can subscribe to the feeds in Internet Explorer 7's Favorites Center, then display them in a Feed Headlines gadget in the Sidebar. Of course, Griffioen has some work to do first; Nutshell feeds don't seem to be compatible with Vista and IE7. But you might have suspected that, huh?