gr> ... and all I did was update from 1.4.1 to 1.4P.
gr> 
gr> uriel:~% top                                                               [23]
gr> top: sysctl vm.uvmexp failed: Cannot allocate memory
gr> uriel:~% ps ajx                                                            [24]
gr> ps: proc size mismatch (25056 total, 680 chunks).
gr> ps: statfs on /proc failed: No such file or directory
gr> ps: fallback /proc-based lookup also failed.  Giving up...

I think you need to compile ps,top,w with the libkvm which
is used to compile your -current kernel.

which I did not find the q and a in:
http://www.netbsd.org/Ports/macppc/faq.html
http://www.netbsd.org/Documentation/kernel/

I found the answer in
http://www.netbsd.org/Documentation/misc/
where starting the line, either following lines.
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w, ps, and netstat do not work after upgrading to a new kernel (top)
------------------------
After changing kernels, 'ps' reports "proc size mismatch" (top)
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Makoto Fujiwara, Chiba Japan