On my site, I have elevated it up the top of every page. Otherwise in 3.07pl1 it only appears on the board index page.
This is the result:
You'll see I removed it from the usual spot, so it's not doubled-up.
It's easy enough to modify overall_header for this change, but I think it might be worth discussing as a core change. This means the 'view unread posts' feature is always visible and within reach of any page.
A more complex further enhancement would be a discreet menu that was on the top of each page, that included all the other search types: view unanswered, view new and view active. It could sit alongside the position I have got 'view unread' in the screenshot. A menu would conserve screen real-estate, but still be easier to access than clicking back to 'board index' in order to find those other search types.