This may be related to #2, but I find modules/classes, very helpful in finding functionality. Someone just asked on IRC if there is a function to determine if a file exists. In Ruby, I would expect to find such a function in the File class, and sure enough, there is a File.exist? function.
This can be done in other ways such as partitioning functionality into files (if the code is the spec/doc), or organizing documentation in certain ways, but it's been my experience that a module/class system makes finding functions easier.
