I'm a recent(last year) oberlin grad. group showers are in only a few dorms, and are simple to avoid if they make you uncomfortable. co-ed bathrooms take a little getting used to. it's embarrasing to go potty while someone of the opposite sex can hear you. two things: first, this, too, is not hard to avoid, second, it's not something you should worry about anyway.
you should under no circumstances let this put you off oberlin. i had a wonderful time there, and i'm not someone who is particularly excited about taking showers with people whose names i don't know.
what you should do is look into the co-ops. if *they* sound really cool, then oberlin is for you. i've never heard of anything like the oberlin co-op system, in college or out. OSCA is a unique and wonderful organization. look into it!