I am amazed at people's naivety when it comes to the Internet! Somehow people think that they can control what's on the Internet. The latest example is Obama1). The Obama team has removed many policies2) from their website see: Agenda vanishes from Obama's transition website as reported by CNet.
Did you put in foot in your mouth on your photo blog
3)? and now wish to retract it?
Did you post a comment on somebody else's website, that now you regret being associated with it?
Did you post what turns out to be embarrassing photos?
Did you post some photos that are not your best work?
Are you posting your new prices, and hope that people will not notice the price increase?
What's on the web, will stay there forever, even if you delete the page from your own web server.
Removing a photo from your web page, will not delete it, many other indexing servers have made copies.
Don't put anything on the web that you will regret days, month or years later.
Don't put anything on the web that you will not be proud of.
Don't put anything on the web that you would not show your customers.