I've asked Joel to include a confirmation box for every erase from the context menu, as in Eraser 5. This is another reason for making that change. There are occasions when one might want to erase all the data on a drive, though I agree that this is probably best not done from the context menu.
Until the next stable version comes out (late 2010 at the earliest, I understand), it will probably be better not to use the drive context menu for any form of erasing; set up a task in the task pane instead. Once the task is set up (< 1 minute for a normal free space erase), it's as fast to use the task pane as the context menu.
David