It really is a bit of a shame that .sit is not very popular on PC - it's simply the fact that WinZIP comes pre-installed on virtually every PC and StuffIt does not. Alladin claims that .sit is typically 20% smaller than .zip and most "real world" magazine tests (and my own experiences) backed this. I know there is a battle about compression filesizes going on, and it certainly isn't worth skipping a well-established format like .zip for an obscure new one which occasionally saves you just a few bytes, but 20% on average is a lot... :-)