Seconded (thirded?, fourthed?). The essential features should be;
Don't waste screen area when no search term is needed.
Make it OBVIOUS to the user that a search keyword is needed when it is.
Don't obscure the MIDDLE page with a dialog box (like Cello does)
Don't Require the user to do anything extra.
I also support the idea of directing all keyboard to the search box.
This has caused problems to naive users here, though it wouldn't be too
bad if the input are was highlighted more obviously.