Also, though synchronization for Palm devices (as if they matter anymore) is included in Ubuntu, you can't sync to an iPhone, Windows Mobile device, or other handheld -- even though these are increasingly commonplace in business. But Ubuntu can access an iPod's or iPhone's photos as if it were a digital camera. (There are hacks out there to support some of these devices for data and music syncing, but IT doesn't want to rely on hacks.)
Essentially, desktop Linux makes sense as the desktop OS only for those employees who do common work in Office and Web apps. But that's a lot of people.
Solving some of IT's control issuesDesktop Linux's app limitations mean that you'll still need Windows PC or Macs for users who require specialty apps. But they also provide an easy way to assert control over the desktops you manage.
Think about it: Most of your malware worries go away, as does the constant effort to stay up with the latest anti-malware patches. You don't need to worry about users installing games, iTunes, or spyware -- those are designed for Windows (and sometimes the Mac) -- so the need to monitor rogue apps is greatly reduced.
Of course, you won't have the same kind of central system management options that you do for Windows PCs. So you'll need to rely on your Linux distro's update manager, as well as your apps. This automated, client-level approach is also standard on Windows and Mac OS, even though many IT organizations don't like it and instead want to validate and apply such patches centrally. The more control you want, the less you'll like desktop Linux (just as you probably don't like the Mac.
But desktop Linux does support basic Active Directory authentication for user access management.
I'm not suggesting every organization chuck its Windows or Mac OSes for desktop Linux. But many companies, government agencies, and educational institutions can chuck at least some of them. Those based on XP -- or Windows 2000, which still has a huge installed base in government agencies -- can look to big savings on licensing, hardware, and training costs.
Desktop Linux and its core productivity apps are solid and worth serious consideration for many of your users' PCs. Try it yourself.