Just found a nice page at the W3C (yeah, now I know this exists since February January). Web Style Sheets CSS tips & tricks. Example 6 is really funny:
Some browsers (IE, Konqueror) have recently started supporting the non-standard properties 'scrollbar-shadow-color', 'scrollbar-track-color' and others. These properties are illegal: they are neither defined in any CSS specification nor are they marked as proprietary (by prefixing them with "-vendor-"). But luckily you can easily disable them.
I don't think designers will be happy with this, but its funny and useful. If you have a browser specific theme you don't want some web author to decrease the usability of your (styled) browser. They already control the 'horrible' intro movies.