This is the only theme I've used for a long time now, so needless to say, I really like it. The simplicity is the most important thing for me. Anyway, have to agree with Paolo, and would like to add two more changes if I may:
1. The white shadow that goes with the bookmarks toolbar item text makes it hard to read the text. I currently use the theme without the shadow (had to edit browser.css) and it's much better to look at.
2. The background of the URL bar when selected is always white. The text itself hanges to blue but not the background as it usually is.The color change is not strong enough and is very tiring for the eye when looking at what is selected and what is not. I tweaked with the css files, but bringing the background change automatically screws up with the edges of the background image of the URLbar. (square background appears around the edges).