I noticed a couple of .DS_Store files appearing in some of the archives that I've been receiving and recognized them as MacOS X files used for display, much like the Windows thumbs.db (created to store thumbnails of files - check the "Do not cache thumbnails" in Tools > Folder Options > View). I looked up more info and here's what I came across:
Under Macintosh OSX .DS_Store holds the information which controls the way a folder will be opened; i.e., the shape and size of the window, the position of the window on the desktop and whether file, folder or icon view has been selected. If you were to delete the .DS_Store the folder would revert to the system default next time it is opened and a new blank .DS_Store would appear (invisibly).
You can disable the creation of .DS_Store files by MacOS X by running this command from the terminal window: defaults write com.apple.desktopservices DSDontWriteNetworkStores true