Do it! We took our son to the MK for a day when he was 7 1/2 months, and we are going back next month for 3 days for his 1st birthday.
We all had a blast! He met Mickey (actually, he knows Mickey from MM Clubhouse and freaked out, in a good way), got his first mouse ears, and loved It's a Small World. He went on just about every ride with us, including Pirates, and we have a priceless family photo from Buzz Lightyear. Mom and Dad intensively competing, bands on the triggers, and baby in the carrier looking wide-eyed straight into the camera with a "what the heck are they doing to me?" look on his face.
I would recommend taking your everyday stroller, b/c our son took his naps in his. Actually, out of all the things I planned for, I did not plan on him taking a 2 hour nap in the middle of Fantasyland (which was fine b/c we got to child swap on 7DMT and Space Mountain).
Also, a front carrier was great. We got a cheaper one just for this trip to use in line and on rides. Support wasn't awesome for me, but it was great having him see everything on the rides and me not worrying about him wiggling around.
We kept our expectations low, but we ended up doing much more rides that we imagined. We also stayed at All-Star Movies, and the baby loved looking at all of the larger than life stuff.