A number of people wrote to whack on me for claiming the Tab key was related to the metal tabs on a mechanical typewriter, saying instead that it is short for "tabulator," a device for making tables. In that sense the key name still makes sense on the computer keyboard, although I wonder if people would have thought that before Word came up with its table feature. On systems with monospaced fonts (and even on Macs with proportional fonts), many people still use the space bar to make tables.
Full Screen Quick Look in Snow Leopard
When viewing files in the Finder in Snow Leopard, instead of pressing just the Space bar to enter Quick Look, press Option-Space to display the selected document in full-screen Quick Look, expanding the preview and hiding everything else that would otherwise remain visible.