There is an important issue with the style sheets we are adding. I have been run into this issue at RTL layout development and lost many hours on figuring out - why the IE layout was broken and finally found http://support.microsoft.com/kb/262161.
We should change the way how we add CSS files to the page to solve this issue. Please keep in mind - since we added RTL support, the RTL people will be the very first running into this issue, but others with many modules installed will run into the same issues. This bug makes development VERY difficult and impossible, while i cannot turn on css aggregation in development.
If we go the following way we can keep the single files, but we end up with "one" style tag only - what finally solves the issues!
<style type="text/css" media="all">