Xfce is a desktop environment that will feel very comfortable to users joining us from the land of MacIntosh. Of the desktop environments, Xfce is the lightest and smallest of the group. So it's also the fastest of the desktop environments. That being said, it's about as derivative as you can get. Mouse, pager, menus, taskbar, widgets. Yawn! If you hate surprises, you'll love Xfce.
Xfce is, however, very efficient and very simple. I could not imagine the new user who would need more than a day to learn everything they need to know about Xfce. It is lean almost to the point of being starved for features. It comes with a small handful of configuration utilities, but unlike other desktop environments, it doesn't have a full suite of every imaginable kind of program. Instead, Xfce runs both the KDE and Gnome suites remarkably well. It's sole innovation is the AppFinder, which will ferret out whatever other applications you have installed on your system and load them into menus.
Just like Gnome's and KDE's panels, Xfce's panel will run in any kind of desktop. Speed is good; while Xfce has a brief delay on start-up, when it's up, it's pretty fast. It is rock-solid, being the least-troubled desktop environment.
Xfce isn't very exciting to look at. It has several window decoration schemes and wallpapers, but no overall desktop themes. It meets your eye-candy expectations halfway. But it is smart and efficient. Given time, it grows on you. Like IceWM, whenever I have stumbled on Xfce on any random distro, I was happily using it without a second thought, but when I left, I promptly forgot it.
Xfce is found in the occasional distro, sometimes even being the default desktop like in Wolvix and FreeSBIE. I recommend Xfce for the office user. It is simple enough that a newbie will be up to speed in no time, light enough to run almost any tool suite without too much burden, and doesn't have so many features that the user is distracted.