Not found!
I find it frustrating to follow a link to a site and then to be told the page is not found. From a technical side, this means a 404 error occured: page not found. Some site replace the stock error page with one of their own, and some include a search box so you can try to find the new location of the page you want.
The most innovative one I’ve seen is generated on Greenpeace’s US web site. Here’s a link that doesn’t work and will get you their 404 not found page.