Thanks for that. Talk about non-obvious. I could swear there's a checkbox for that on my dual head Hackintosh that is not present on my MacBook when I plug an external screen. Or it could be me (that time we used the MacBook as a fallback of the fallback — dedicated DVD player died + suddenly no 5.1 sound on XBox360, so I was quite enraged).

Edit: ah, after checking, the drag-the-menubar thing is actually written in the prefpane, and there's no checkbox. Silly me.