We have separate machines in our house and it does make it easier. However, there is nothing on my computer that I wouldn't want or let my wife see. If you are hiding things (other than a gift purchase for B-day or Christmas) then you really should reevaluate your marriage as there is a lack of trust. My wife/best friend of 16 years can look at anything she wants on my computer.
That's for sure. When I get secretive about my e-mail or computer, she knows I probably got her something.