That's what I'd like to say to every client that forwards me these type of compressed files.
Nothing sucks more than having a 600mb sit file expand over a period of 3 hrs ! (on a fast mac)
What's more insulting is the low ratio compression that the majority of users use when they compress these. Ok. you made me wait 2 hrs to decompress your sh*t. Why is the uncompressed source only %2 bigger than the compressed sit file? Use the built in Mac OS "Create Archive of" instead you morons. Hint: right click on the file/folder to compress them