I have been trying to compile the source from the main bitcoin tree and ran into a problem with the qt4-mac macport not being Mountain Lion ready yet.
It's not terrible to fix it so that it will build, but it blocks the ability to build bitcoin-qt from scratch on 10.8
I found the info necessary to compile qt4-mac here:
https://trac.macports.org/ticket/35313Then in the bitcoin code I had to make one change to src/qt/qtipcserver.cpp so that
+static void ipcThread(void* pArg){}
+static void ipcThread2(void* pArg){}
where defined as empty functions.
Then once I had all the ports installed the bitcoin-qt cllient would build and run.