I have X.5 running fine on a dual 2.0GHz G5 at work, but the dual 1.8 GHz machine that I have just started to use at home (which came to me bashed and which I had to disassemble & rehabilitate much more fundamentally at the level of the processors, heatsinks, etc. before it would boot at all) will tell me to 'shut down or else' about once an hour under X.5.

Hope it's not going to keel over completely in a month or so. That would be a bitter blow. But it is comforting to know that the behaviour can be seen in other G5 machines/ PPC hardware.