Read the whole article at http://www.masteringemacs.org/articles/2013/12/29/whats-new-in-emacs-24-4/.
He had also written a similar article for Emacs 24.3 (current stable version),
which can be found here.
New Settings that I am using
I have already setup the
electric-pair-mode options also look interesting, and I have set these
up (I was using
skeleton-pair for the auto-pairing function till now).
M-s . (isearch-forward-symbol-at-point) is going to be very useful. It
essentially replicates what
C-s C-w does, but having a single key-stroke is a
little easier. A closely related command
M-s h . (highlight-symbol-at-point)
also looks to be useful. This is especially handy with the
C-x SPC (rectangle-mark-mode) finally allows replacing CUA for me.
Eshell now has even better support for visual commands; i.e., commands
which expect a terminal. See the options
eshell-visual-options for details.
New Interesting Modes
dired-hide-details-mode is also nice. It has already replaced
dired-details for me.
superword-mode looks to be useful (especially for programming Ruby, where
underscores are usually used to separate words in an identifier).
The new file notification system would be very useful, except that it does
not (yet) work in OSX (bummer).
Other Default Settings of Interest
desktop-auto-save-timeout is going to be a life-saver. The related option for
desktop-restore-frames finally does what I want.
The new electric-pair settings
electric-pair-open-newline-between-pairs do exactly what is expected.
Ruby-mode has some interesting updates, especially for indentation.