Another mapnik install, another set of issues… I had a brand new OSX Lion install on my imac, but had a few issues with the brew install of Mapnik as I wanted to link it to Cairo.
See the Homebrew Mapnik instruction page

brew install python
Change the .bash_profile to add export PATH=/usr/local/bin:/usr/local/sbin:$PATH.

brew install git
brew install postgresql
brew install icu4c
brew install proj
brew install libtiff
brew install gdal --with-libtiff=/usr/local/lib
brew install cairo

The real problems came with cairomm.

brew install cairomm
which led to those errors

Then the issue was that the symbols from cairo were not found.
"_cairo_xlib_surface_get_xrender_format", referenced from:
Cairo::XlibSurface::get_xrender_format() const in xlib_surface.o
ld: symbol(s) not found for architecture x86_64

One trick I found was to check what was required for the cairo library:
pkg-config --cflags --libs cairo

It complained about missing dependencies. I ended up installing also
brew install fontconfig

I ended up with this new Formula:

and cairomm installed properly.

Then finally
brew install mapnik