I'm using LibreOffice 3.6.4.3 on Ubuntu 12.10.

I use cell color and cell borders to group and distinguish groups of cells in my spreadsheet.

I need bold horizontal borders every 4 rows. This is a pain to do in the current version because you can't specify "embolden the borders on every nth row". So I do it manually, for enough of the spreadsheet as I need to deal with.
(This formatting is undone if I drag the fill handle to copy formula(e) across multiple rows.)

Please add a method, perhaps similar to the one used in FrameMaker, that allows the specification of two levels of formatting: (a) the one we currently have, and (b) a separate one for every nth row/column. This way we could have groups of n columns/rows with bolder borders every nth row/column and different colors every nth row/column. This kind of grouping by color and/or border is really useful for making columns and rows of data more readable.