Stardock has released a desktop organizer tool that I found very useful, I think that doing something similar as a Compiz plugin would improve your desktop funcionality

reference:
http://www.stardock.com/products/fences/

Compiz recently updated the desktop wall switcher so that, when switching workspaces, the windows of the old workspace slide away and the new windows slide in. This replaces the old functionality, where the whole desktop would slide to the selected workspace. The new plugin has been updated into Jaunty.

This will make it much harder for new users to understand workspace switching. This new plugin does a terrible job of communicating the metaphor of multiple workspaces, instead giving the impression that it is minimizing windows but not listing them at the bottom.

One of the big problems with Nvidia's proprietary drivers right now is that they give you no control over the power settings. As a result, the card is often at it's lowest power setting, which makes Compiz and other composited apps look terrible. One way to solve this (aside from bludgeoning the Linux driver folks at Nvidia) is to trick the card into waking up when an action requiring compositing is anticipated.

For example, to switch virtual desktops I use Ctrl + Alt + Arrow (up, down, left, right). In this case, the graphics card could be told to ramp up on detecting Ctrl + Alt. The principle can be applied to any key combination longer than one, though I can't honestly say what gains in visual performance there would be.

This would ideally be a user controllable setting, with the option to let it be controlled by current power state (battery or AC).

transparent objects are very nice and it's always present in mockups end new themes. Unfortunately, when we are using transparency, the text in the foreground is often messed with the background(part that would be hidden if the actual element was not transparent). Sometime it's impossible to understand what there is.
it can be solved by reducing the contrast or blurring the background (only under the transparent part). my suggestion is include wherever the transparency is used the option to blur the background on compiz. even more sophisticated effects can be taken to blur.