I think it has to do with your cat's temperament too. My kitty .Asia is very laid back. As long as she's fed and cuddled, she's happy. She jumped into the crib a few times when we first set it up (before .Aly was born) because it was new, but hasn't since we've brought her home. The appeal wore off since she'd already checked it out.
She doesn't seem interested in .Aly at all, or threatened by her. (but she'll jump out of her skin if the baby sneezes!) but if she were to ever act hostile towards her, I would strongly consider finding a new home for her.
Basically, we didn't treat .Asia much differently when the baby came. We didn't make any rooms "forbidden", so she wasn't more curious about them and trying to sneak in. And I would hold her and let her look into the crib at the baby so she wouldn't feel the need to investigate unsupervised. We haven't had a single problem, and we have a very happy well-adjusted cat. But then again, my kitty rocks, so who knows.