I just booked a January trip to the US with some sightseeing in Colombia on the way home. I started with AA.com (American Airlines) but was quickly told that there system could not book a multi-city trip online at this time, I was told call them. Surprisingly it only took about 10 minutes to reach a helpful human. But getting my choices and enterring my information through her was very slow and time consuming so I switched to Expedia.com.
I tried several times to book my multi-city trip but I wasn't satisfied with the choices I was being offerred, for example, there was no non-stop from BOG to EZE being offerred. So I tried to book separate one-way legs instead of a multi-city trip and lots more options appeared like the missing direct flight to EZE and a late morning JetBlue from FLL to CTG. I ended up with 3 one-way reservations and most surprisingly the cost was 30% less than the best multi-city price!
The other surprise was that a car rental reservation was non-changeable, non-refundable. I've never seen this before.