The computer I'm writing this on came with Windows XP. It probably wouldn't run Windows 7, so is it reasonable to expect it to run the latest Linux desktops? Gnome 3 and KDE may need fairly recent hardware to run (well) but there are Linux desktops designed to run on older, less powerful hardware. I've looked at Crunchbang before which is indeed nippy on my older laptop, ten years old this year. Today I've been trying out XFCE 4.8 on Debian Wheezy from a Live USB. It zips along even from the USB, so I have no doubt it would be fast if installed- just about ideal for this or any other XP era machine.
The only real drawback with XFCE is that it is a 20th century desktop paradigm. Some see limitations in that paradigm, others comfort. The limitations are a potential dog's breakfast in the notification area, redundant icons with duplicated functionality, inefficient use of screen space, and inefficiency in a cluttered window switching mechanism.
It seems XFCE has tried to get away from the Windows 95 paradigm with the main panel now positioned at the top of the screen, and a second panel acting as an application launcher at the bottom of the screen.
The desktop is still very much menu driven.
With a full screen window open, the bottom panel restricts the space available: set it to auto hide.
I got rid of the bottom panel because of the redundancy issue mentioned previously: you can't switch applications using the icons in the bottom panel, so they have to appear again in the top panel as window buttons. If you really want the Apple look, a real dock like Docky might be a good idea- it works with XFCE compositing.
It's very easy to change the look of XFCE. Here's what I did, first with the BSM simple theme.
A bit of a Windows 7 look here with buttons only for windows switching, and programs automatically grouped.
The old fashioned window switching method in XFCE handles the GIMPs modal windows well.
Here's a full screen application, not quite as efficient as Epiphany in Gnome 3: the title bar takes up space unnecessarily. It doesn't seem to be possible to undecorate the window as it is in Openbox.
Here's another theme, my own modification of the Axiom theme, going for a Gnome 3/Adwaita look, but without any extra theme engine dependencies- this is supposed to be a light desktop.
Unlike Gnome 3, menu driven of course.
A full screen application again.
I've kept the notification area in these screenshots very minimal, but it is possible to put just about anything you'd want there: weather, email notification, kitchen sink...
In summary, XFCE is a great desktop for slightly older computers, or computer users who prefer a slightly older paradigm. With a bit of effort, it's possible to give it a more modern look and feel.
The only drawback to mention is a fairly serious bug which prevents removable media like USB drives being mounted, and the computer being shutdown normally. With Wheezy coming up to release soon, this bug will have to be fixed, so if you're thinking of installing, it might be worth waiting for a few months.
UPDATE: I found a solution to the above problem.