I’m only familiar with Beryl, I’m well-read about KDE4, but I don’t know anything about Windows Vista, but I’ll still give my opinion on DE as a whole.
The only thing that is less good in Beryl is the window tackiness modifier button (stacking), the rotating cube, which makes the choice between the Tables a bit more convenient, and a convenient preview of the windows while Alt-Tab and hovering the mouse over the application in the taskbar.
All special effects are superfluous and created just to popontovatsya, that even the cube has a dubious expediency. because you can organize everything easier and more convenient.
Little is known about KDE4 yet, but it is good to switch between desktops (just from the table with screenshots)
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What would you like to see new in DE:
1) To start, do not make their number strictly limited, and the ability to rename them quickly
2) Ability to save "blank" desktops (templates), so that it would be possible with one click / one key combination to open the desktop with many applications with a predefined convenient location of windows
3) It would be nice to have the opportunity to have “an integrated desktop, i.e. broken into several independent areas
4) The ability to add to the background of the table some elements of monitoring, or just the current screenshot of some application / part of the desktop / whole desktop
5) Ability to split the panel into several parts. Ability to make them hidden, as well as sub-panels hiding in other panels
6) It would be nice when switching between tables to see their names, display all desktops in small screens, but at the same time see a larger screenshot
7) And for some reason I also like radial menus (for example, as in Maya4), so it would be nice to be able to choose between the normal and radial menus (something that pops up on the right-click)
8) “(Desktop) application”, i.e. tab / (desktop) on which there will be no menus, and nothing else at all but the most running application
Well, at least something like this:

(I apologize for no quality, but this is nothing more than an outline)
(PS not loading on Habr 4 personnel * .gif. What to do?)
one:
“*” - transition to the global desktop manager
“Arrow” - open the list (4) of desktops in the form of named tabs
2: taskbar with a list of current desktop applications
3: the main menu with the ability to open the “quicklunch” (Q) submenu, hide completely, or open the “big window” of tasks (with a list of applications of all workstations)
4: tabs list of desktops
“Black frame”:
On the left Desktops - a list of desktops,
Monitoring on the right - list of monitoring areas / tables / applications from which you can choose some to add to the background of a desktop
Bottom Preview - just a preview of the desktop, or monitoring
Well, the area over which I just did not think