Like this? http://operawatch.com/news/2007/04/how-to-edit-advanced-settings-in-the-opera-browser.html

And the government would have prior art claims over the Mafia!

I'd say that a lot of installations are for corporate environments which use legacy applications (both Intranet and web-based) which rely on IE6, or which are not updated due to the fear of incompatibility. I use only Opera and Firefox at home (and on work computers when permitted by system policy), but I've had IE6 on various work laptops (both for my firm and for clients) due to these kinds of issues. Web-based clients with issues included a time and expense system (critical in a professional services firm), an older iteration of Salesforce.com, and all kinds of home-grown applications.