In Photoshop CS4, we’ve changed the way that you close Panels - right mouse click (Ctrl-click on Mac with a single-button mouse) on the tab and select Close or Close Tab Group. If you pull a panel out of it’s tabbed group and float it freely, then a close button (x) appear - simply click to close.
If you tap the Tab key (to hide the panels), they will be automatically revealed when positioning the cursor at the edge of the monitor (similar to a roll-over effect). To toggle off this feature, choose Preferences / Interface / Auto-Show Hidden Panels.
To free up more screen real estate in Photoshop CS3, we introduced collapsible “iconic” panels. However, they remained open after clicking on them. Now, in Photoshop CS4, you can choose to collapse the panels automatically by right clicking on the panel tab, or by selecting the Preferences > Interface > Auto-Collapse Iconic Panels. Basically, you show the panel (by clicking on the icon), pick you options, and when you click anywhere outside of the panel, it will automatically collapse.
And one last tip: the Tool bar can be relocated and even “docked” to the panels on the right side of the screen. Click-drag the grabber handle at the top of the the tools, and when you see the solid blue line next to your panels on the right, release the cursor to “dock” the panel. Or, if you prefer, you can move any of the panels to the left side and dock then with the tool box. You can also relocate the Options bar for example you may want it at the bottom of the monitor or on a secondary monitor.