I swear by those vacuum-sealed space bags for my clothes. You'd be amazed at how much you can squeeze into those things!
This sounds like an awesome idea for staying with friends, but I can't see myself asking to borrow a vacuum from housekeeping for a resort stay or bringing a second empty bag for puffier clothes on the return trip. Little did I know, there are several products that offer the same seals with no special suction necessary like the Roll Up & Go travel set with a carry on and suitcase-sized sack inside. Have you used this style for anything other than storage's sake?