To expand on Matthew Savage’s comment, do this:
brew install imagemagick --disable-openmp
and it starts working again. No need to edit the files. (I’m not sure if thats what he’s actually saying or if he’s saying remove the flag, but the above homebrew command works for me on OSX 10.6)
If you already have imagemagick installed then
brew uninstall imagemagick && brew install imagemagick --disable-openmp
brew upgrade -f
no longer reinstalls, so you have to uninstall it first.)