I am using spotlight search on my MacBook, and am excluding a few folders from spotlight search. My problem with Apple's method of excluding the folders is that excluding them actually calls attention to them. If I let a friend use my computer or something, and they happen to end up in that preference pane, all they have to do to go to the folders is double click on them.
I tried this tip, however it seems not to work under OSX Lion.
Also, please don't tell me to just log out, or lock my computer when I am away. That is something I have made a habit of doing, however I still allow people to use my account (browse iTunes, etc.).