Does not IE8 InPrivate Browsing and InPrivate Filtering do the same thing ?
Not the same.
If too many people click the button this could be a significant issue for Internet companies. Many depend on tracking for even minor features.
I used it a couple of times, and from what I remember, it can be quite
annoying to deal with it not keeping track of histories and the like
that would be handy to keep around for the session.