> This is helped by a great feature of the environment (Emacs/SLIME) which provides cross-referencing tools, for example, I can place the cursor on the name of a function and ask “where is this defined”, and it jumps to the place of the definition, which could be in my own code or in third party code. But I can also ask “where is this function called” or “where is this variable referenced”. This is extremely useful for code refactoring and it beats every “modern” IDE I've seen.

wow, rly? you have this in Eclipse (and probably every 'modern' IDE out there) for every language.