I have happily donated my way to gold today!
I have a site I'm working on in 3.3.2... works fine! I tried 3.4.01 today and it breaks pretty well, I'm afraid. I saw the caution re upgrading to 3.4, but the external/internal css/js makes no difference. If it helps you any, I'm going to insert before and after pictures.
Before (with 3.33.2): http://tinyurl.com/ntwtfh
After (with 3.4.01): http://tinyurl.com/mykojr
Hope Flynn can lay hands on the new version ... It looks like it will be killer!