Well it is an unlabeled, anonymous editbox. One can only guess by seeing its width that it's a search field, and not a field that takes in a page number to which you want to jump... I can understand how someone misses this bit; the search link is logically before the editbox. English readers read left-right, top-down.

There's visual noise there that's easy to ignore. The forms in the cells of that table at the top of a forum category could be grouped better to indicate their functions IMO (perhaps not easily, Firefox's DOM Inspector for this site scares me :)

Lastly, the message on the downed search page doesn't indicate that you can still search, and the newspost regarding the issue got pushed down...

DeViLBoI? :D