The way I understand MWI it basically is a Schroedinger-all-the-way-down approach, and measurement just becomes the act of getting your measurement apparatus (and hence your own brain and mind) entangled with the system. Decoherence, likewise, is just a matter of getting your system entangled with its environment.
One of my lecturers used to say that the main problem with MWI is that it looked like all the maths was done on the back of a napkin. I'm inclined to agree. It's very easy to explain Many Worlds with the example of a single particle and a single observer, but once you start throwing in a large number of mutually interacting particles, several observers, and take note of the fact that the observer him/herself is made up of multiple interacting particles, it suddenly becomes horribly complicated. As far as I know, nobody has ever done a many-worlds treatment beyond the simplest possible examples.
One of my lecturers used to say that the main problem with MWI is that it looked like all the maths was done on the back of a napkin. I'm inclined to agree. It's very easy to explain Many Worlds with the example of a single particle and a single observer, but once you start throwing in a large number of mutually interacting particles, several observers, and take note of the fact that the observer him/herself is made up of multiple interacting particles, it suddenly becomes horribly complicated. As far as I know, nobody has ever done a many-worlds treatment beyond the simplest possible examples.