Took DS at 8 months (last Dec). He loved it. We also went with him at 6 months. We did lots of the rides - he loved Its a Small World, Winnie the Pooh, Peter Pan, walking through Mickey's house, Buzz Lightyear...
He didn't like the dark rides as much - Haunted Mansion or Pirates - but he would generally sleep on the darker rides (or nurse).
The 3D movies - we learned to consider the noise level - Mickey's PhilharMagic was just too loud for him, so I left part way through.
At DS - he loved Playhouse Disney (mostly watching the older kids dance around). He liked the Backlot Tour, etc. Mostly, he was happy if he could be held, and the scenery was changing. He was happy just in the stroller people watching. Overall, both trips at 6 mo and 8 mo were really easy with him, and if he needed a break, we went back to the Resort, or stopped in Baby Care to nurse or just rest. He also loved the characters (esp. the fuzzy ones) and I got a ton of great pictures.
He may not remember it, but I had a great time with him, and have pictures forever.