My internet service is provided by Rogers. They have this annoying "feature" where if you type in a url in the address bar and the site doesn't exist they throw up a Yahoo! search page, passing in whatever you typed.
Why do I find it annoying? Because A) if I wanted to search I would have searched, and B) if I made a simple typo I can't just change it the address bar because now it is the address of their search page. I vaguely remember there was some noise about this a couple of years ago and it went away. Now it is unfortunately back.
Funny thing is they let you turn off the search page, but it still hijacks the address bar anyway - it replaces what I typed with "http://www20.search.rogers.com/not_found" and shows a mimic of the page my browser would have shown you anyway. What possible value does this add? Yeach! Actually it is worse than that because anyone who customized their browser's behaviour on a 404 will find it doesn't work anymore.