Did you ever "forget" to tell someone part of a story so they wouldn't be upset? I have found through experience that honesty is the best policy, no matter how upset the other person will get, they will get more upset if they find out the truth.
At work if someone messes up, people will respect you if you are up front and honest about it.
At home, if you go out with friends, and not tell your significant other who exactly was there, generally that's a sign that something's going on.
With friends, if you need to tell them something that can potentially hurt their feelings, the best policy is to be honest and gentle when confronting them. If your friend found out you were hiding something from them, they'd probably be even more angry with you, and may even possibly end the friendship. What is worth more to you? Hiding something that can be discussed and cleared up, or taking the risk of losing that person forever?
Today I got home early enough to watch an episode of Dismissed on MTV...that is where that tangent came from. I hate reality tv.