Is there any interest in my expanding the list of probes? Ruby has quite
a few more than function-entry and function-return, to give some
examples of what is possible:

http://dev.joyent.com/projects/ruby-dtrace/wiki/Ruby+DTrace+probes+and+arguments

I think that adding probes that correspond to PyTrace_LINE and
PyTrace_EXCEPTION would be straightforward and worthwhile. PyTrace_C_*
may also be worthwhile, but you can probably accomplish similar things
with the normal pid probes if you know the C function names (although
something like printing the name of a raised exception will probably
require a dedicated probe).

Adding probes to replicate what the LLTRACE configuration option did,
but dynamically, might be interesting.