For example, the card with Tinkerbell on the front (yeah, technically she's not a princess, but she sure acts like it some times) has a message that goes something like "To be young forever, head for the second star on the right and straight on 'til morning" on the front, while inside it says "That's where they hide the Botox."
I highly reccommend that anyone that purchases that card not give it to anyone under 40.
The Little Mermaid card says something like "Birthdays are like living underwater... You can do it, but you'll get all WRINKLY" in an adorable font. Sleeping Beauty's says "It's your birthday, so party, party, party! ... You can always sleep, sleep, sleep later" or something like that. I can't remember Cinderella's really well, but I do remember it sounded a bit racier than I would have expected from a Disney product. Maybe it's me.