It's certainly not something I'd advise; dynamic CSS is a path fraught with danger, and I'd like CSS to be kept unsullied...
However, I do not think CSS should color embedded Ruby code by default. Is that used a lot?
I'm not planning to use it dynamically, rather I plan to use it statically to generate a css file. I want to use erb so I can embed variables in the css file, etc. I actually have a template for a .css.rb file that embeds the css in a here doc which can now have embedded erb using my addition to the css bundle (the Ruby bundle already allows css embedding). I then load the here doc into erb and generate a .css file with the same name next to the .css.rb file when the file is executed. It's a pretty neat way to be able to use variables and simple expressions (for colors, height / width, etc) in a css file.
A bundle with a template and some commands, etc for working with a .css.rb file would be pretty easy to create once the css bundle supports Ruby embedding.
Matthew