We have taken DS for his 1st, 2nd, and 3rd birthday. In December, we are planning to go back with him - he will be 4, and presumably his 4 month old sister will be joining us (we are due the end of july)!!
I am actually quite looking forward to traveling with the baby at this age - I think it will be easier than traveling with a 7 month old (4 months means no baby food, just bottles/nursing, and much easier to entertain than a crawler!)!!!!
We always get airplane seats for our kids, so we'll have the carseat on the plane and will bring our inglensina zippy stroller for the airport and when we need a single in the park. I also plan to rent a double stroller (BJCM) for our entire stay since we wont own our own and will need it depending on the time of day we are in the parks. We have taken the Zippy to the parks the past 3 years and I have loved it - it collapses really well so it was easy to bring on transportation but has all of the features that we needed for DS to be comfy in his stroller for the occasional nap as well as our needs to be able to store 'stuff' (and not have it tip over when he got out - which is why we dont bring our Maclaren Quest!).
That being said - if we werent
DVC members, I'm not sure we would go (despite the fact that I am dying for a vacation!). Having the washer/dryer in our room is really what sealed the deal - the idea of bringing a weeks worth of clothes for a newborn would kill me!
Also - if you do decide to bring a baby, make sure you have a good baby carrier that you both like! We own a baby bjorn that just doesnt work for us - lots of back pain and baby isnt that comfy either...We are goign to try out an Ergo carrier with this little one - I've heard that its more comfy for baby and parent!
Lastly - we have traveled with family and friends for parts of our trips the past few years...I have to say - its not necessarily easier!! We are deliberately NOT inviting anyone with us for this years trip as it will be much easier for us to care for our children and react to their schedule needs if we dont have to worry about anyone elses plans/agenda!! We still managed to go on all of the big rides thanks to parent swap/fast pass/single rider lines and have had a great time even though we dont go on them together!! We also did get a babysitter one night for our anniversary when DS was 1 - again a better plan for us than leaving our child with family that was there...at least the babysitter was a professional and trained to deal with kids and first aid (heavin forbid it was needed!)! Definitely not the case for my BIL/SIL!!