Learning keyboard shortcuts is the sign of a proficiency in any program. Sometimes you might get so good with keyboard shortcuts that you barely ever touch a mouse. Using keyboard shortcuts also makes your workflow much quicker once you get the hang of them. But sometimes you don't know every keyboard shortcut.
ShortcutWorld is aiming to make a comprehensive repository of lists that will have every keyboard shortcut for any given program. Already they have a pretty good list of programs going. Currently ShortcutWorld offers complete lists on Firefox, Winamp, Microsoft Word, Excel, Powerpoint, Fireworks, XP, Google Chrome, CS4, and Outlook. That's a pretty good start!
With this batch to start off with, I'd expect ShortcutWorld to grow considerably over the next few months, unless there is a competitor out there that does better. There's a LOT of programs out there, and cateloguing them all would be impossible, but it'd still be fun to try. The selection of programs makes sense for now, though, because these are the most used programs in the universe.