We took DS when he was 5 months last September. It was great. I loved the baby centers they were wonderful, a great place for changing a baby and the nursing areas were nice, dimly lit and rarely had anyone else in them so he didn't get distracted while eating. Our Mei Tei (type of sling) was wonderful, it made it a lot easier to carry him around and we didn't need to take him out for rides, unlike the stroller. So if he fell asleep in it, no problem we could both go on rides still without one of us having to wait for the other (we didn't do any rides he couldn't do). That being said we also had a stroller which was nice for our longer park days, since after 3 or 4 hours he got heavy (he was a big 5 month old though and 19 pounds at the time).
We did take it slow, which wasn't a big deal since we had been the year before. He loved meeting characters, he adored Minnie's and Mickey's noses and kept trying to eat them.
He was really portable at 5 months which was nice, we did have to make sure he got some move around time in the evenings. He was army crawling at that point though and he had plenty of room to explore when in our room. He also adored the pool, we took him swimming every evening and it was probably his favorite part of the trip.
That being said I would definitely do a trip again with a 5 month old, it was a lot of fun, though we were not comando and watched baby for when he had had enough of the parks and was ready to go.
We were even able to use cloth diapers the whole trip which was nice, we were afraid they might have ended up as too much work, but they worked fine especially with the nice changing centers at the baby care centers.