Private browsing is browsing the Web without leaving any traces of your activity: No caching, cookies, history, or form data. Porn viewing and illegal activities come to mind, but the feature - currently present only in Safari - has a number of good uses.
Ok, who am I kidding: it's only for porn.
In any case, I Started Something notices two of Microsoft's trademark filings, which indicate that something akin to private browsing might show up in the next iteration of Internet Explorer. The filings were for:
CLEARTRACKS
IC 009. US 021 023 026 036 038. G & S: computer programs for accessing and using the Internet and the world wide web; and computer programs for deleting search history after accessing websites
INPRIVATE
IC 009. US 021 023 026 036 038. G & S: computer programs for accessing and using the Internet and the world wide web; computer programs for disabling the history and file caching features of a web browser; and computer software for notifying a user of a web browser when others are tracking web use and for controlling the information others can access about such use