We flew with United last December - Via Chicago O'Hare, though.
Problems on arrival due to customs computer system being down

- the queues could've rivalled Disney's most popular attraction in the highest season - believe me! Just one of those things - really annoying but beyond anyone's control!
Problems with their internal airline - Ted - not enough cabin crew to allow our plane to fly on schedule. Finally arrived in Orlando about 3 hours late.
When we checked in to return, we got terrible seating arrangements for the internal flight (Orlando - Chicago) despite being at the airport well in advance of departure time. DD was 3 at the time and she was seated by herself FOUR rows behind me and DH was FOUR rows in front of me!

When I asked if they could help by atleast letting DD sit with ONE of us, I was told "no - but once you board the plane, she's cute - get her to flutter her eyelashes at the folks she'll be sitting with - I'm sure they'll move if you ask them to!" Strangely enough, the couple who checked in after us got the two seats together, next to our little one.

Luckily, they were actually in our travel party but this was unbeknown to the ground staff as they didn't even have the same family name!
The long-haul portion was a bit better - our party of 9 was split over 3 rows with 5 seats in each row - atleast we could all see each other and DD got to sit with me!
The good thing about them though was that they let us check the stroller in at the plane door and we got it straight away as we disembarked the aircraft!
Although most of our problems were out of human control - weather and stubborn computer systems - the seating thing really bugged me!