I took a trip alone with my daughter this past December, and she was only 9 months old! I really wanted to take her to see the Christmas parade (she loves characters!) and the Osborne lights (yep, loves lights too) and figured she's only going to be this age and be so excited she jumps up and down at a Christmas light once and I'm not back in work yet so I might as well take advantage of my time with my daughter. We both had a great time and I would definitely not hesitate to take her back alone. My husband was able to get away for the weekend, so he joined us for 2 nights (baby and I were in our room at ASMu by noon on Friday and stayed till Tuesday afternoon and DH arrived around midnight Friday and left Sunday afternoon), mostly cause he wanted to come, but partially cause I thought I'd get bored alone with an infant.
It wasn't too scary for me also because I went to DL when she was 6 months with my mom on a convention so I was alone in the parks all day while my mom was in meetings. At that time my daughter loved the Pooh ride (and at DL there was NEVER a wait for it) so she and I rode that over and over.
The only thing I was a bit nervous about was staying in the room alone with the baby everynight, just cause you never know when a weirdo will find out you're alone and stuff. I told the CM when I checked in that I wanted a room on the main path, as close to the main building as possible since I would be alone most of the trip and she was very nice and gave me a room in the 1st non-preferred building. I had flown alone with her a few times already so that wasn't an issue.
It was great to have my husband there (as always) but I have to admit it was nice to be there alone with the baby too. We moved at our own pace and saw only the attractions I thought she'd like best (which we did with my husband, but he also had to ride Space Mtn, ToT, TT, and RnRC while we waited).