There are only three other people that I would allow to use my Mac for more than 5 minutes without me shadowing them. It seems stronger with my laptops than desktops, but only barely, and has nothing to do with expense or being afraid that they'd read my documents. I share clothes, books, DVD's, etc. so I'm not entirely selfish. In general, I find my relationship to my MacBookPro similar to the one I had with my old Rapidographic drawing pen. In the case of the pen, the nob actually conforms to your hand. In the Mac, I don't know. It's intimate in a very tangible, yet strange way. How many people do you allow on your computer?