I decided to not mess with .vimrc but simply relearn all the shortcuts. It was painful at first but now it works great, I use vim just as productively as before, just pressing different physical keys. And I do consider myself a semi-proficient vim user. Of course, going back to using vim with a qwerty layout would probably be hell, whereas I can sort of manage normal text input with qwerty :)
I had the same concerns at first, but then I read this and other posts like it and never looked back: http://sermoa.wordpress.com/2011/12/16/colemak-and-vim-but-w.../
I was always curious about switching to an alternative keyboard layout. Unfortunately I switch between a bunch of different computers and OSes and just haven't found the energy to make such a switch.