Ok, thanks for the info.
I was creating sort of a QuadTree by hand, adding and removing objects from the world on demand.
It works quite Ok, but it lags a bit when loading the new objects, I assume it is my own fault since I did not optimize it properly,
Something I also noticed is that removing the object from the world is much more efficient than setting it invisible. Does it sound reasonable?
I am targeting Nexus One level hardware, but I want it to "run" on a G1, I know it is terrible for performance.