"There was an engineer over at Yahoo who documented the debugger in much greater detail and clarity than in the perldocs(IMHO)."

That would be me, and thanks. I'm always glad to talk abut debugger internals (though I admit to still being kinda unclear about some of it. That's some pretty convoluted code), so /msg me if you like.

As far as developing your own commands, I did a hack called Devel::Command that lets you play around with your own debugger commands. Essentially it patches DB::DB at startup to insert a check for user commands first. It's pretty easy to use. As an example, Devel::Command::Viz adds a viz command that uses GraphViz::Data::Structure to draw pretty pictures of your data (Unix-like systems only, but Windows patches really really welcome!).