I do this. I hang them by the rear rim, so the back of my garage looks like a butcher's store room, with a row of bikes hanging like sides of beef.
A very serious cycling-nut pal was visiting once and left his bikes on the roof rack overnight rather than risk 'pulling the rims out of true' by suspending the whole weight of the bike from one rim. I was bemused.
He, in turn, thought me mad to do what I did (and still do).
I've been doing it for fifteen years with no ill effect. Does my pal have a point, or is he a velo-hypochondriac?