Cactus Game Design Message Boards

I use them for my Dominion cards--because each card only gets played every sixth game or so, and everyone does quick overhand shuffles, which is pretty non damaging.

Man, for Dominion cards I have a much stronger recommendation.  Regular card sleeves of any quality just won't hack it.

And yes, penny sleeves are clear and somewhat flimsy.  They'll do the job in a pinch but they won't mask any markings on card backs.  I tend to promote their use in things like booster draft.