Looking at another posting, it seemed like some dynamic libraries were wrong. I went ahead and removed (renamed) the incorrect ones and then created symbolic links to the correct mac libraries into the <alf install>/common/lib folder. It was just these three libraries for me.
ln -s /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ImageIO.framework/Versions/A/Resources/libJPEG.dylib /Applications/alfresco-4.2.c/common/lib/libJPEG.dylib
ln -s /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ImageIO.framework/Versions/A/Resources/libTIFF.dylib /Applications/alfresco-4.2.c/common/lib/libTIFF.dylib
ln -s /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ImageIO.framework/Versions/A/Resources/libiconv.2.dylib /Applications/alfresco-4.2.c/common/lib/libiconv.2.dylib