It's a shame Cartoon Network never really "expanded" on this idea and make a TV special or episode out of all this. Crossovers are BIG attention getters, even if they are all just characters owned by the same single company. It's worth seeing and I wish they would try an idea like that.
I always liked the "bumper shorts" that involved mixing of the characters like Kaz from Ami Yumi meeting Juniper Lee. Or the Dog from Juniper Lee asking Velma from Scooby Doo and Mandy from Billy and Mandy if they needed anymore sunscreen and stuff like that.
I think they could have a gold mine with stuff like that. My favorite one is easily the most amusing "team ups". It's Raven from Teen Titans and Mandy sitting on a train and just being absolutely quiet and monotone as usual:
Mandy: Nice talking to you.
Raven: Whatever.
I don't even like Billy/Mandy and I can totally appreciate the humor in that.