In Apple’s quest to simplify the user experience, they windows status bar in Mac OS X Lion. This definitely makes for a cleaner appearance when looking at folders, but if you actually like to know how much disk space you have available at a quick glance, it’s kind of annoying.
You can show the Status Bar by hitting Command+/ or by pulling down the View menu and selecting “Show Status Bar”
The folder status bar actually shows more than just available disk space, it will also give you the active folders item count, and give you the slider to adjust icon size. If you have no idea what I’m talking about, here’s a screen shot highlighting it: