There is an old bug in OLE that MS sort of fixed with Office 2007 on Windows - 13 years after introducing it. The problem is that if you copy a big picture, such as a JPEG photo, and paste it into Office, it also stores an uncompressed full size preview as a bitmapped image (BMP). The workaround on Windows is to use Insert -> as image instead of pasting, which works around the bug. I once received a 137 MB Powerpoint in the mail from a certain manager who knew he'd get chewed out but didn't want to bother splitting it. I recompressed it and sent it back - 600 kB. It's that bad. Even if you only have a few pictures, it's worth checking for that.