I've always said it like 'Yoo-hoo' but the Wiki page says it should be 'oo-hoo' after the German name for an Eagle Owl.

Also good work to the Germans for that if it's true. We should name more animals onomatapaeically (sp?) in this country...well in reference to the noise they make. Who needs 'owl' when we can calle them tuhwit-tuhwoos?