Sounds like a job for Emacs!

Install Emacs through your distribution's package manager.

Emacs comes with Remember Mode, which does pretty much what you want. (Note that there's a lot of complication in the Emacs Wiki that you don't care about, because it's for older versions of Emacs. Remember Mode is bundled since Emacs 23.)

To start taking a note, run the following shell command:

emacsclient -a "" -e "(let ((pop-up-frame-alist \`((window-system . x) (display . \"$DISPLAY\") ,@pop-up-frame-alist))) (remember-other-frame))"


(Having just -e "(remember-other-frame)" doesn't work if Emacs isn't already displaying a window due to a bad interaction between server mode and frame creation.)
You can add other frame parameters in that list, with the syntax (NAME . VALUE). For example, to set a smaller height:

emacsclient -a "" -e "(let ((pop-up-frame-alist \`((window-system . x) (display . \"$DISPLAY\") (height . 8) ,@pop-up-frame-alist))) (remember-other-frame))"


Bind that shell command to a key in your window manager or desktop environment; each has its own way of doing this, so I can't describe them all.

Emacs will start if it isn't already running, and a new Emacs window showing an empty file will pop up. When you've finished taking that note, press Ctrl+C twice. If you want to change that key binding, you can do it in your .emacs, for example to use Ctrl+Return, use this code:

(require 'remember)
(define-key remember-mode-map [C-return] 'remember-finalize)


If you want to save some text from another application, copy it to the clipboard and run this command (which you may want to bind to a key as well):

emacsclient -a "" -c -e "(remember-clipboard)"


With this command, you need to press Ctrl+C twice, then close the window.

The notes are saved in the file ~/.notes (each new note is appended to that file). A header containing ** followed by the current time is automatically added at the beginning of the note.

To browse the notes, just open ~/.notes in your favorite text editor (such as Emacs).

If you want to save the notes to a different file, add a line like this to your ~/.emacs:

(setq remember-data-file "/path/to/notes/file")


What Remember mode lacks out of the box is a really convenient way of deleting a single note. You can of course select the text and delete it. Here's a function to delete the current note, plus a bit of infrastructure to bind it to a key when browsing the notes file. Put this code in your ~/.emacs.

(defun remember-current-note-extent ()
  (save-match-data
    (save-excursion
      (end-of-line)
      (let ((beg (search-backward (concat "\n" remember-leader-text))))
        (forward-char)
        (cons beg
              (if (search-forward (concat "\n" remember-leader-text) nil t)
                  (- (point) 1 (length remember-leader-text))
                (point-max)))))))
(defun remember-mark-current-note ()
  (interactive "@")
  (let ((bounds (remember-current-note-extent)))
    (set-mark (car bounds))
    (goto-char (cdr bounds))))
(defun remember-delete-current-note ()
  (interactive "@*")
  (let ((bounds (remember-current-note-extent)))
    (delete-region (car bounds) (cdr bounds))))

(defvar remember-notes-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map "\C-c\C-d" 'remember-delete-current-note)
    map)
  "Keymap for Remember Notes mode.")

(define-derived-mode remember-notes-mode text-mode "Notes"
  "Major mode to browse Remember notes.

\\{remember-notes-mode-map}"
  (require 'remember))
(add-to-list 'auto-mode-alist '("/\\.notes\\'" . remember-notes-mode))


Take quick notes without interrupting current activity
I've been told it is important to use matching DIMMs when installing memory to take advantage of the 128 bit throughput. I'm looking to buy a new 27" iMac (mid 2011) which has 4 memory slots. If I put matching 2x2GB in 2 of the slots and matching 2x4GB in the other two slots, will that reduce its throughput or cause any problems? 

Do all 4 have to match or do each set of 2 need to match?
