An interesting solution by Simon Schönbeck that also works in Google spreadsheet.

Suppose you have some strings in a sheet with different lengths. All you need to do is to create a second column, select the first cell, insert the function =LEN(A1) and then drag down:

Now, by selecting both columns, go to Data→Sort Range and sort by column B. Since column B contains numbers representing the length of the strings in column A, column A will be sorted as well by string length.

The pairwise difference between cells in a column can be calculated using the OFFSET excel command:

Applying the formula to all rows (by dragging), will result in the following table:

You can also use ABS in the offset formula:

=ABS(OFFSET(C2, -1, -2, 1, 1)-OFFSET(C2, 0, -2, 1, 1))

in order to avoid negative values.