I was watching my host/mentor try to fix my broken perforce client when I saw him do something really cool. You can search previous commands in bash! Hit ctrl-r and type a substring, ctrl-r again to see next result, etc. (ctrl-anything seems to kill the search, and tab selects.)

Working at Google I periodically have “Whoa how did you do that” moments, and its kind of cool being surrounded by people who are really really good at what they do.