The Dash in Ubuntu 6.04 had decided to come up in full screen mode every time I opened it. This wasn’t what I wanted. After a period of Googling (during which I was surprised to discover that most questions on the Dash were asking how to make that the default behaviour) I found the command I was looking for:
gsettings set com.canonical.Unity form-factor Desktop
Entering this in a terminal forces the Dash to adopt my preferred fashion, taking up the top left of the screen only.