I mainly use MAMP when developing web applications locally. MAMP is great because you can easily switch from PHP4 to PHP5, it's very easy to configure, and everything is built into one package. However I do have a second development environment setup on my machine. I also use the package that Marc Liyanage made available, but I only use this environment if I am dealing with PDFlib, because PDFlib does not work with MAMP. It's lame having projects in two different development environments depending on if I need PDF support.
Good news. I just came across this work around in MAMP that is actually documented in the PDFlib handbook. For some reason, about a year ago google did not pick this text up in the documentation when I originally searched for a work around. Now I can finally have one development environment that gives me PHP4, PHP5, and Xdebug and not have to wonder which environment I have a certain project.
To cure the problem with MAMP comment out YLD_LIBRARY_PATH in /Applications/MAMP/Library/bin/envvars.