I was struck by how XP-like Ubuntu is. And that's a good thing. It took me very little time to find where standard functions are, given the similarities. In fact, it's a much easier transition. The menu structure is clear and not hidden. There's none of the "I'm so complex I must hide myself in gewgaws" nonsense that Microsoft has convinced itself, in Vista and Windows 7, makes a good UI but in fact further complicates an already hodgepodge user interface. (Gluing feathers on a platypus won't make it fly.) Users can get to work without guessing what Microsoft thinks they ought to do.
Adding Hewlett-Packard and Brother network printers was trivial -- easier than in Windows and about the same as on the Mac. But I did have to install drivers for the Brother's fax and scanner capabilities, and these required command-line installation via the Terminal. Using an external USB media card drive was also no biggie; Ubuntu detected both the drive and the SD card I inserted, saw it contained photos, and asked to launch a photo management app. You can expect to come across compatibility issues with more exotic hardware, but most business PCs don't typically include that class of consumer-oriented gear.
Well-suited for office workers, but not specialty users. After basic compatibility with PC hardware, the big criticism of desktop Linux is the state of its apps. There's good news and bad news here. Ubuntu comes with the Mozilla Firefox Web browser and the Evolution Mail client pre-installed, as well as OpenOffice.org's office productivity suite.
Firefox is my preferred browser, but if you depend on ActiveX controls for your company's Web apps (which you should not in this multibrowser, multiplatform world), the lack of Internet Explorer could be a deal killer. The Evolution Mail client is fantastic; it easily connects to Exchange Server for mail, calendar, and contacts, using LDAP and Outlook Web Access. The UI is similar to Outlook's but simpler. And in a move that should shame Microsoft, the Evolution Mail client is more compatible with Exchange than is Microsoft's Mac client, Entourage. (One example: I could set an away notice, which I cannot do with Entourage.) You can also run Mozilla Thunderbird if you're POP-oriented, though Evolution Mail also supports POP and IMAP.
OpenOffice is a sound alternative to Microsoft Office, but I spent most of my time with the free IBM Lotus Symphony, which is a slightly better productivity suite than OpenOffice, in an evaluation. It's simply more refined and will be easier for Office users to adapt to, even though it lacks the database and drawing applications that OpenOffice has. I'm sure there are features in Word, Excel, and PowerPoint that Symphony and OpenOffice can't match, but you can bet that for 80 percent or more of your "knowledge workers," sales staff, and so on that Symphony or OpenOffice will do the job.