If you visit Google Images in the UK, you get a little promotion for Google Image Labeler that reads:
Want to help improve Google Image Search? Try Google Image Labeler.
The link to Google Image Labeler links to http://images.google.co.uk/imagelabeler/. But if you try going to that page, up comes a page not found error.
The requested URL /imagelabeler/ was not found on this server
The US version of the URL does work at http://images.google.com/imagelabeler/.
Funny that a Google promotion link is linking to a page not found error.
Forum discussion at Cre8asite Forums.