James Duncan Davidson has a great overview article (that needs no further explaining from myself), titled Sandboxing Rails With MacPorts. Another similar article can be found here.

My problem is that I work on a lot of projects that use ImageMagick / RMagick, and that’s not discussed here.

No worries, I’ll install ‘em and give it a go:

sudo port intall ImageMagick
sudo gem install rmagick

CRAP! I don’t know what happens for you, but ImageMagick installs perfectly for me, and then RMagick craps out and dies something like this:

/opt/local/lib/ruby/gems/1.8/gems/rmagick-1.15.9/./lib/rvg/misc.rb:321:in `get_type_metrics': 
unable to read font `(null)' (Magick::ImageMagickError)
 from /opt/local/lib/ruby/gems/1.8/gems/rmagick-1.15.9/./lib/rvg/misc.rb:321:in `render'
 from /opt/local/lib/ruby/gems/1.8/gems/rmagick-1.15.9/./lib/rvg/misc.rb:696:in `text'

Now, for the solution I am going to give all credit to Jakob Skjerning, because I found the solution on his site after doing some Googling.

Do this instead:

sudo port install ImageMagick
sudo port install rb-rmagick

Done. Works. Thank goodness.