I voted no, although I sometimes use a 3D-Desktop, but not one of the mentioned ones.
I sometimes use the good, old 3DDesktop, I even have a shortcut for it and installed K3DDesktop (but don't have it active) for it.
I've been thinking about installing one to try, but I haven't gotten around to it yet. If it adds to productivity, I will surely keep it. If it's purely eye candy, then I can do without.
In some subtle ways it probably does add to the productivity a bit, and it feels much more natural to us humans because the desktops responds to you as if it were some sort of a life-like object with many other objects laying around. It is also aesthetically pleasing which is good for those working with a computer a lot.
However, all of this can be easily spoiled if it glitches as it does for me. My 3D acceleration works quite fine, but in beryl there are still ocassional breaks and lags as well as tediously slow scrolling in applications. This could very well be because free ATI drivers I'm using are still experimental, but it's enough for me not to use it regularly.
However if you've got Intel 950GMA chip I hear it works just fine, as Intel makes their own free drivers.
most of it would be eye-candy, but someplugins are quite useful: for window switching scale beats all. I move the mouse pointer to the bottom-left corner of the screen or press pause (neither is the default configuration) and all windows from all desktops appear neatly lines up. Takes away all the problems of the bliss that is overlapping windows. The beryl window switcher is slightly improved compared to those of conventional window managers in that it shows you the window you'd switch to.
A chap I met at the Linuxtage in Chemnitz had beryl set up to place him in the cube... I don't like that too much, but he said it helped him keep all four desktops in mind at once.
I would do it if I had a higher-performance system with a powerful videocard. I would love to use it as a lure for me to get more people to use Linux. However, I only inherit PCs from my office. They're pretty decent, but not the latest greatest stuff. As a Linux advocate, I just can't justify going out to spend $2K on a new PC or laptop. I mean, one of the greatest points I want to make with people about Linux is that I can get sensational performance with it on substandard hardware.
$2K is way above what you need. laptop bought on eBay in February for ~â‚¬300 - can run beryl, not the really fancy stuff and not brilliant performance in real use, but it works.
You might want to start putting subjects on your posts...