Are social networking sites costing us our privacy?

[kittycat]

With facebook, MSN Spaces, Myspace, Twitter, Bebo, Classmates and other such networking sites growing and becoming more and more popular, is the internet becoming too intrusive?
There has been a new trend of "creeping" where people look at your profiles for updates, and can find things you'd posted long ago and may have even forgotten about now. It has even gotten to the point where people have lost jobs over photo's of them drinking and such on the internet.
An example would be the trouble that Miley Cyrus (Hannah Montana) got into for making a silly face that was interpreted as racist and degrading, in a photograph which was later posted online.
With PerezHilton.Com we are given access to celebrities lives, and criticisms of them.
I'm just curious, how do you feel knowing that a frenemie or an ex could be creeping you? Do you do anything to prevent it?
Yes of course I realize that by posting something you are putting it out there for the world to see.
But what if there is happy news I want to share with my friends, such as an engagment, or an invite to a party, that I am not posting for the "creepers" of the world to see?
I am not asking because I have any particular issues with these sites, or the content of them, my question is simply to ask your opinion on the growing trend of "creeping"