We took DD for the first time in January, when she was 11 months. We've been 6 more times, since then. We take her on everything without a height restriction.
To be honest, she seems to be rather indifferent to most of the rides and attractions. She likes all the stimulation and the variety of things to look at, but the only time she really lights up with excitement is when we let her run around in one of the play areas, like the Boneyard at AK, or when we take her to the pool at the hotel. Also, she enjoys FOTLK and Playhouse Disney, and claps along to the music.
Her 3 year old brother, on the other hand, can't get enough of WDW. In between trips, he studies the park maps and plans what he wants to do the next time we go!