The Leopard news of the moment is that Xar will be baked in. Xar, or eXtensible ARchive format, is just what it sounds like, a new way to compress files. You're thinking, 'Aren't there lots of ways to do this already?' Yes, but as this page entitled 'Why xar is interesting' explains Xar has some big things going for it. Firstly, it keeps metadata (like file type, MP3 data, and the like) in a separate file so you can tell lots about a compressed file without having to uncompress it. It also compressed each file separately, so if you Xar a folder each file is compressed separately.
Xar is already available for download, if the more technical amongst you would like to take it for a spin.