Many of the convenient syntax shortcuts for Word 2007’s equation editor are, to my knowledge, completely undocumented. A discussion of most of the commands for different symbols and operators is available here. In addition, I have compiled a list of shortcuts that I have discovered mainly through trial and error.
Update: While the symbol shortcuts aren’t documented per se, you can access them (and add new ones) by starting a new equation (alt+=), selecting Tools under the Equation Tools/Design menu (top left), and clicking on Math AutoCorrect. Murray Sargent’s Math In Office blog has some tips on adding new symbols.
