I would say it depends on
a) How well you know them. If you've never seen them at all in person, it might be VERY weird...and even beyond that it would depend on how much interaction and what it's been...unless you genuinely ARE friends, hold off on the "friend birthday" cards. You know? A few meetings at the stage door do NOT make you BFFs.
b) How you get it to them. If you will be
seeing a show on the day or just before and they at least know your face and you haven't been stalkery before, if you're seeing the show it might be ok to give it to them there. Otherwise send to the theatre. I definitely agree about the home address. If you know them well enough they've given it to you, they probably won't be wigged out by a card. If they haven't given it to you, a card sent there might freak them out a little.
If the birthdays are easy to find, that's another factor. If it's kept pretty quiet and you've found it out, that's definitely a freaky factor.
Experience live theater. Experience paintings. Experience books. Live, look and listen like artists! ~ imaginethis
LIVE THAT LESSON!!!!!!