I figured the crossover would be some alternate reality storyline featuring characters from our comics drawn by the artists involved. We should probably set up some sort of brainstorming session on IRC, AIM or MSNIM to come up with some kind of general plot or idea we want to follow. It would be good to have an organized plot and host it here at Turbocool. While the Panel Jam was an interesting idea, the less organized comic coops tend to fizzle out after a while.
Anyway, it would probably be good to find out who's interested first and then move on to planning out a story. While swapping comics is an interesting idea as well, I think some of us have already done guest strips for other comics in the group and I personally don't find it to be much of a "Turbocool" project as it is an individual project. That's my 2 yen on the matter, anyway.