If it weren't for vim, I would have definitely considered switching. I know you can map keys and all, but, it just doesn't make sense going through all the hassle. Are there any bi-layouters out there?
I find that I don't have to actively think about what layout I am typing in, it just flows. I imagine bilinguists have a similar experience.
I chose Colemak primarily because it doesn't mess with common shortcuts (Bottom-left keys "qwarzxcvbm" remain the the same positions).