I'm excited about the possibilities of having stuff like gravity and forces to play with. I can actually use those in game ideas. I'm also excited about the possibility of getting rid of my collision detection system and using ODE for the as well. My current system is extremely simplistic which is great for card games but it definitely can't currently handle anything fancy. Plugging in a library that magically brings me up to the fancy level is cool.
My only concern is that ODE works best with fixed length updates. That just means having a regular interval between physics "frames". That really shouldn't be a problem for my engine since each system runs independantly of each other but there are always potential hiccups while running due to other things going on in the OS. I hope it doesn't totally look like ass when one of these happens.