We have taken our DD3.5 to Disney 4 times and now have our 5th trip booked. Each visit has been wonderful for different reasons. The first trip she was 6 mths. There were plenty of rides we could take her on. She LOVED all the characters and we got tons of great photos. On the 2nd & 3rd trips (1 year & 1.5 years) she was scared of the characters but, loved the rides. On our last trip (2.5 years) she loved it all including standing in line with her autograph book.
The comment most people give us about taking her is that "she will never remember it". That is not the point. I totally disagree with people who plan their vacations solely for their children. This is our vacation too and we LOVE Disney. And although she may not remember the early trips, we sure will and it has made wonderful memories for my DH & I to share for the rest of our lives!!