Bullet has some really great features over ODE; soft body physics, particle physics, and hardware acceleration among the top.
After talking with a Crystal Space developer about this, I put it on my list of things to look into when PySoy is a bit more mature. However, a Debian packager's decision has accelerated these plans.
ODE is not designed to be installed as a single shared library, it has many build-time options which radically change it's behaviour - such as whether the library uses single or double precision, or whether to calculate gyroscopic force. As a general rule, distributions stick to the defaults when packaging as much as possible, but Debian (and thus Ubuntu and other Debian-based distros) ship a single system-wide library with non-default compile flags (Double precision) that would result in sub-par performance, network sync issues, and in some cases bugs in games.
Debian could have shipped four or eight different versions of the ODE library, such that games could be linked against the one it was designed for and work as expected, or ODE could have been designed to build both a single and double precision library with the other options as runtime flags, but instead we game developers are caught in the middle.
We fought this battle before with Soya, for some time actually, and in the end Soya had to ship their own version of ODE embedded in the source and statically linked to get around the problem. Even then it was an issue to get the package including a static ODE included. It's a battle not worth fighting.
While Bullet also supports building as double precision, it's an option so rarely used that no distro builds with it (Gentoo doesn't even have a USE flag to switch it), and given that Bullet is currently not packaged for Debian it'd be easier to add it as a new proper package than fight Debian packages to improve their build of ODE.
I am not looking forward to working with Bullet's incomplete C-API, likely having to fill in some gaps as we work on it, nor writing the Vala bindings for Bullet, but it'd be a lot faster and fun - not to mention resulting in new features.