Reopening this performance thread: i'm getting the same perf issue due to colliders.
Just out of curiosity: Michael, have you considered at some point skipping physics altogether? At least for a 2d only interface, physics cost seems overkill --> it's fairly easy to raycast in 2d on a set of quads. I'm considering modifying ngui to support that, at least for my complex interface needs.
Before i embark on that, I'd appreciate any thoughts you might have about this...