Development buildout for 1.2:

[buildout]
index = http://download.zope.org/ppix
parts = 
    interpreter
    geos
    testrunner
develop =
    src/Shapely

[geos]
recipe = hexagonit.recipe.cmmi
url = http://download.osgeo.org/geos/geos-3.1.1.tar.bz2

[interpreter]
recipe = zc.recipe.egg
eggs =
    Shapely
    numpy
interpreter = labpy

[testrunner]
recipe = zc.recipe.testrunner
extra-paths =   
    ${buildout:directory}/eggs/numpy-1.3.0-py2.5-macosx-10.5-i386.egg
eggs =
    Shapely
script = test-shapely
environment = geosenv

[geosenv]
LD_LIBRARY_PATH = ${geos:location}/lib
DYLD_LIBRARY_PATH = ${geos:location}/lib

Save as buildout.cfg in a virtualenv, install  zc.buildout, bootstrap, and run "buildout".