While waiting for your answer,
daemonfowl, a tiny little bit of searching found that in July,
a problem was reported to bugs@ regarding segmentation faults with threaded applications in -current,
on G3 processors. I don't know what your processor is, but there are 333Mhz G3s.
A search of the commits made in recent months did not highlight any recent G3 specific fixes for this.
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If the problems are occurring
without any packages installed, then the problem is not FAQ 15.4.1 related and is something else ... perhaps you too have this problem that was reported in July, or perhaps you have a hardware problem. You can test this by installing 5.1-release. If you still have segfaults while on -release, then I would consider a hardware problem a possibility. If 5.1-release runs just fine, then you can rule out hardware as a root cause.