64 bit OSX 10.5 support has been promised for a while, but I finally managed a couple hours ago to fix a segfault issue in libSingular that made Sage segfault instantly when any multivariate polynomial ring was created. If you check out the 64 bit OSX port page in the wiki you will see that there are currently 35+ ticket listed which need to be fixed. I have patches for all of them, but the quality is uneven and a couple of those patches need to be redone. So it will take a couple more weeks until all those issues are sorted out and polished patches are merged into the official tree.
I have put together a binary [OSX 10.5 x86-64 only]. It is rather hefty at 0.5GB, but I have left a substantial number of hand build spkgs in the dmg more or less by accident. If you plan to build a 64 bit build of Sage on your OSX machine you should wait a couple more days until 3.0.2 is released which will contain the vast majority of fixes. It is even likely that there will be an official 64 bit OSX 10.5 binary, but currently there are 24 doctest failures. Some are trivial to fix, others are caused by the notebook not working due to _ctypes being broken. There are other small issues with pexpect and a couple additional small issues, but overall we are in pretty good shape. On exit OSX also complains about a couple "Non-aligned pointer being freed", but that seems to be mostly cosmetic and will be fixed soon since I got a good idea what is causing this. We will hopefully be at a point where we can call OSX in 64 bit mode fully supported soon, but there will be some more work involved before we are done.