I’m not unguilty of this; I once relegated the search form to an archives page in a previous design incarnation, a technique similar to that employed by CSS Wizardry:

The CSS Wizardry archives page with search box.

We tend to search for something on a website instead of navigating through menus, or when the menus have failed us: placing the search form within the site’s architecture makes us go through the whole menu process to begin a search.

The IA search box is hidden in the footer.

Search forms are best placed top right (ahem); failing that, they should be easily available on every page of a website. Anything else is illogical.