I'm studying up for a TV segment I'm taping tomorrow on engagement rings and trying to memorize the different ring descriptions, prices and designer names.. There are six that I really should know by heart, but to be safe I'm writing the information down on notecards.
I'd rather refer to a card on set than make something up or say I don't know the answer to a question.
While it would be nice to recite your own vows by heart or toast the bride and groom without a printed speech, it's better to have a note card or paper with the words you want to say on them than forget what you wanted to say and be stuck with the mic.
No one in that room will hold it against you or look down on you for referring to your notes. This is a very important day and it's better to get the words you want to say out correctly than have to make something up on the fly.