Emacs Text Scale – Fix Line Numbers Column Shrinking with Text-Scale-Adjust

M-x goto-line (M-g g or M-g M-g) gets you to the beginning of the target line. Then you can use C-u 8 right to move to the target column. Note that this puts you in column 8, because Emacs numbers columns from 0, except that the command line option +LINE:COLUMN numbers columns from 1.

If you want an Emacs command where you can type 2:9, here's some code you can paste in your .emacs that allows you to write it as an argument to goto-line. Note that the code is only minimally tested in Emacs 23.

(defadvice goto-line (around goto-column activate)
  "Allow a specification of LINE:COLUMN instead of just COLUMN.
Just :COLUMN moves to the specified column on the current line.
Just LINE: moves to the current column on the specified line.
LINE alone still moves to the beginning of the specified line (like LINE:0)."
  (if (symbolp line) (setq line (symbol-name line)))
  (let ((column (save-match-data
                  (if (and (stringp line)
                           (string-match "\\`\\([0-9]*\\):\\([0-9]*\\)\\'" line))
                      (prog1
                        (match-string 2 line)
                        (setq line (match-string 1 line)))
                    nil))))
    (if (stringp column)
        (setq column (if (= (length column) 0)
                         (current-column)
                       (string-to-int column))))
    (if (stringp line)
        (setq line (if (= (length line) 0)
                       (if buffer
                         (save-excursion
                           (set-buffer buffer)
                           (line-number-at-pos))
                         nil)
                     (string-to-int line))))
    (if line
        ad-do-it)
    (if column
        (let ((limit (- (save-excursion (forward-line 1) (point))
                        (point))))
          (when (< column limit)
            (beginning-of-line)
            (forward-char column))))))

The easiest way to do this is with the rectangle commands.

Go to the first line of the buffer (or more generally the first line where you want to insert text) and move to the column where you want to insert the text. Go to the last line and move to the same column (there's no built-in way to do that). Type C-x r t (string-rectangle) and type the string you want to insert.

You can use the following function to move the cursor to the same column as the mark:

(defun move-to-mark-column ()
  (interactive "@")
  (move-to-column (save-excursion
                    (goto-char (mark))
                    (current-column))))

If you want to move to a column by number, there's move-to-column: C-u 42 M-x move-to-column RET. Unless you bind this to a key, it's shorter to move to the beginning of the line and then by character count (Home C-u 42 Right), but this can move to the next line if the count is too high, whereas move-to-column leaves you at the end of the line in this case. Also move-to-column behaves differently if there are tabs or split lines.

If the point and mark aren't on the same column, they're opposite corner of a rectangle. The rectangle command affect all the characters inside that rectangle. string-rectangle erases the rectangle and puts the specified text on each line instead. C-x r d erases the rectangle. You can also copy-paste (C-x r M-w, C-x r k, C-x r y to copy/kill/yank) and insert or fill with rectangles (C-x r o, C-x r c to open/clear with spaces), and more.