Taken from Gizmodo:

IE 8 Could Get "Porn Mode": Would it Change Your Mind About IE?

What is the best way for IE to gain market share back from Firefox? Porn. That's right—when it comes to the internet, the answer is always porn. You know it, I know it, and apparently Microsoft knows it because there are rumors floating around that they may incorporate a private browsing feature, a.k.a "porn mode," similar to Safari (Firefox pulled the feature from 3.0) that would allow users to thoroughly cover up their smutty tracks from anyone who might be checking their browsing history.