Code is always problematic - especially as the "code" tag only gets the first line in a code block, and that leaves quotes as about the next best option.
Not sure if I would like automated code highlight - css / html forums often get lots of massive code dumps, and automated highlighting may possibly exacerbate the visual "clutter".
I like the suggestion of line-numbering. Better implementation of the code tag would be great. The ability to manually colour lines/comments was a great tool, but I noticed it wasn't available when I tried to use it a few days ago.