Our Mac demos are set up in such a way that no matter what people do to them, every time the demo user logs out, things go right back to the way we want them. To this end, one of our Apple tech reps created a little shell script that is called at logout, and is referenced in /etc/ttys. If you take the reference out and reboot, the little shell script doesn't get called, and you can make changes to the demo account and have them stick. This is useful if you, say, install new software.
This little trick is now broken in Leopard.
By "broken," of course, I mean that there's a different, probably easier way to accomplish the same goal than fucking around with with shell scripts and system files, but I'm buggered if I can find it, and so I can't make Leopard play nice like I could Tiger. The upshot is that BOINC is temporarily on hold until I can fix the demo user problem so that I don't bork the system in the process.
Besides, the Mac Pro was kinda disappointing IIRC... I mean, it's a fucking dual Woodcrest Xeon, FFS, and even factoring in the fact that it's only on for half the day, it still seemed to underperform compared to some of your quads. I personally blame Mac OS for not being as cycle-efficient as its proponents claim, although that's a particularly PC claim to make.