We went in January with our then 5 month old DS. We had some doubts, but they quickly went away. DW and I both work full time so spending the entire week with our new son was fantastic.
DS is never fussy so we didn't worry too much about how he'd react or handle things. It was funny though that on the drive from OH from about 6am to arrival at WDW at 8pm he did not sleep. We thought oh well he'll sleep the next day. We went to DTD and resort-hopped the monorail line, then had dinner at Ohana's, still no naps. The 2nd day at AK he fell asleep in the snuggli on the Kilamanjaro Safari ride. It was hilarous, his little neck all bent over and totally bouncing around but it could not wake him, for the lack of naps finally caught up to him.
It was super-slow when we went (our car was the only one in Pantere Place's at PO-R parking lot during our stay), therefore I noticed we got a lot of attention from CM's and characters. 2 different Mickeys, a Minnie, and a Tigger held him for photos at different points during the week.
We only noticed him really paying attention to a couple of things; the Lion King show at AK, Pooh Ride at MK, and Journey into Your Imagination at Epcot. What he really liked (and still does) was the CM's from other countries at Epcot (mostly) that had strong accents or broken English. This amazes him. He recently enjoyed some extra attention from the busboys and busgirls at a Chinese restaurant.
One thing we never even thought about on our previous WDW trips was this. The thing we enjoyed the most was eating out every day with our baby. Sure we eat out at home (mostly faster meals like Ruby Tuedays or Applebees), but it was nice to have some good, long meals at nice restaurants with DS. We would never think of taking a baby to a place like LeCellier at home, or Wolfgang Puck's, but at WDW you can. Our DS didn't fuss, but if he did so what, look and listen around, probably a half dozen kids/babies somewhere in the restaurant are fussy at one given time but no one notices or cares.
Enjoy the extra attention from CM's, characters,and other guests. The smiles from strangers when they see a baby still amazes me.