Today, I inadvertently found a gem in Eclipse 3.4. Inside the Java Editor, you can right click on a method, and choose "Show in Breadcrumb" and a breadcrumb trails is shown in the first couple lines of your editor. Very Handy, especially since it works for most Java elements. Also handy because it offers quicker navigation than clicking to expand folders in the package explorer. However, I didn't like that it was taking up a couple of lines of space, so I wanted to turn it off. After trying a number of things, including Google, Eclipse help, and Preferences, I found NOTHING about how to hide the breadcrumb.
Finally, I tried this:
Customize Perspective, choose the Commands tab. In the Available command group, choose Java Editor Presentation. The Toolbar details shows the button for Toggle Button, which looks like a folder with a C in a circle with a black triangle on top of it.
I so rarely use the toolbar. I guess that's why I didn't think to look there first.