Personally, I use Exclude Regular Expressions that I figure out in a text file and just past the lot in “Edit as text” mode.
For example, this “Edit as text” value should exclude the a users’s “Videos” and “Downloads” folders on either Windows 98/XP (the Documents and Settings stuff) or beyond (the Users stuff):
-[.:\\(Users|Documents and Settings)\\[^\\]*\\(Videos|Downloads)\\]
To use it in the regular “Exclude regular expression” field just remove the leading “-” and the surrounding “[]” so it would be:
.:\\(Users|Documents and Settings)\\[^\\]*\\(Videos|Downloads)\\
The way I built those expressions was the use the folder tree to select examples of what I wanted to get rid of, use “Edit as text” to see the raw content then convert it to regular expressions so it would apply to all users (or all folders).