emacsのバッファ名を賢く付ける方法を教えてください。

uniquify.el を使ってはどうでしょうか。

(require 'uniquify)
(setq uniquify-buffer-name-style 'post-forward-angle-brackets)

Documentation:
*If non-nil, buffer names are uniquified with parts of directory name.
The value determines the buffer name style and is one of `forward',
`reverse', `post-forward' (the default), or `post-forward-angle-brackets'.
For example, files `/foo/bar/mumble/name' and `/baz/quux/mumble/name'
would have the following buffer names in the various styles:
  forward        bar/mumble/name  quux/mumble/name
  reverse        name\mumble\bar  name\mumble\quux
  post-forward   name|bar/mumble  name|quux/mumble
  post-forward-angle-brackets   name<bar/mumble>  name<quux/mumble>
  nil            name  name<2>