I was playing around in Inkscape again and this time I came up with some liquidy/glassy bars. I think any of these would look pretty sweet as a theme's progress bar. Just imagine them swirling around...
My Inkscape SVG file is available to download here if anyone is motivated enough to do something constructive with it.
In the screenshot you will notice the completely grayscale bars at the top (which is how they look in the SVG file) and below are the same bars with a simple color layer placed over top in The Gimp. Originally, I imagined the "swirls" being a different color from the bar itself, which is easily done with the SVG file.
Unfortunately, I have no plans to implement this into any sort of theme as I am completely lacking in QT/KDE programming skills. However, if you would like to code this up, I am more than willing to help in any way that I can.
*** Please note, this is not a working theme. This is just a drawing of what I think would make a pretty sweet little widget. ***