For me, it really depends on the show.
For a comedy where the jokes are what makes the show (Spamalot, Ave. Q, Book of Mormon), I wouldn't want to go in being TOO familiar. I went in knowing practically every word to every song in Spamalot without having ever seen it and think I would've enjoyed it a lot more knowing less about it. Knowing when and where and how every joke lands wasn't as fun as hearing the jokes for the first time could've been.
For revivals I tend to either know everything about the show and don't mind or to learn everything I can about the show since the resources are available. It's usually the excitement of seeing the revival of the show live for the first time or the performances that are getting me into the theatre.
For new works, I like to go in cold, knowing nothing about what's going to happen. I knew a *little* too much about N2N when I saw it and was slightly disappointed and then vowed to never expose myself to too much about a new show before seeing it.
"These rabid fans...possess the acting talent to portray the hooker...Linda Eder..." -The New York Times